If you're traveling internationally, you might need a visa, which is an endorsement on your passport indicating that you may enter a country. Americans don't need visas to enter 116 countries – including 26 in Europe – for short-term tourism, business or layovers on the way to a non-treaty country. However, some popular destinations such as China and Brazil do require U.S. citizens to obtain visas.
Some countries apply the principle of reciprocity in their visa policy. A country's visa policy is called 'reciprocal' if it imposes visa requirement against citizens of all the countries that impose visa requirements against its own citizens. The opposite is rarely true: a country rarely lifts visa requirements against citizens of all the countries that also lift visa requirements against its own citizens, unless a prior bilateral agreement has been made.
I would say a tourist visa (6 month) is best because a fiance visa limits your time and is not one that can be renewed like a tourist visa. You can renew a tourist visa for 6 months. It does not always get approved but it is something that is possible with the tourist and not with the fiance visa. Now if you plan on getting married as stated in the fiance visa then in…

The main reasons states impose visa restrictions on foreign nationals are to curb illegal immigration, security concerns, and reciprocity for visa restrictions imposed on their own nationals. Typically, nations impose visa restrictions on citizens of poorer countries, along with politically unstable and undemocratic ones, as it is considered more likely that people from these countries will seek to illegally immigrate. Visa restrictions may also be imposed when nationals of another country are perceived as likelier to be terrorists or criminals, or by autocratic regimes that perceive foreign influence to be a threat to their rule.[77][78] According to Professor Eric Neumayer of the London School of Economics:
This document may be denied for any number of reasons. People with certain infectious diseases, for example, may be told to seek treatment for those diseases before a visa will be issued. They may also be denied to people who could potentially strain the system of the country they are visiting: for example, someone without enough money to get by might be denied a visa out of concern that he or she could rely on public assistance for help.
Kuwait,[128] Lebanon,[129] Libya,[130] Saudi Arabia,[131] Sudan,[132] Syria,[133] and Yemen[134] do not allow entry to people with passport stamps from Israel or whose passports have either a used or an unused Israeli visa, or where there is evidence of previous travel to Israel such as entry or exit stamps from neighbouring border posts in transit countries such as Jordan and Egypt.
An East African Single Tourist Visa is under consideration by the relevant sectoral authorities under the East African Community (EAC) integration program. If approved the visa will be valid for all five partner states in the EAC (Kenya, Tanzania, Uganda, Rwanda and Burundi). Under the proposal for the visa, any new East African single visa can be issued by any partner state's embassy. The visa proposal followed an appeal by the tourist boards of the partner states for a common visa to accelerate promotion of the region as a single tourist destination and the EAC Secretariat wants it approved before November's World Travel Fair (or World Travel Market) in London.[96] When approved by the East African council of ministers, tourists could apply for one country's entry visa, which would then be applicable in all regional member states as a single entry requirement initiative.[97] This is considered also by COMESA.
You need a valid passport before applying for a visa. The visa application process may take several weeks and generally must be completed before leaving home. For many countries the application and fee is the same for either a tourist or transit visa. A typical process for obtaining a visa is to complete an application and send it to the country’s embassy along with your original passport, a passport photo, the required fee and any other required documents. Additionally a transit visa application may require documents that verify that you will in fact be leaving the country within the required time period. Each country’s unique visa requirements are found online or by contacting that country’s embassy. Some countries like Colombia, Japan and many European countries do not require a visa for shorter stays.

Whether you are applying for the first time or renewing your visa, you will use the same application process (please review How to Apply, above). Some applicants seeking to renew their visas in certain visa classes may be eligible for the Interview Waiver Program (IWP) which allows qualified individuals to apply for visa renewals without being interviewed in person by a U.S. consular officer. Review the instructions on the website of the U.S. Embassy or Consulate where you will apply to determine if the IWP is available and if you qualify.
On what basis would she be able to adjust status once in the U.S.? Of course she shouldn't do this. If immigration officials even *think she entered the U.S. on a tourist visa with the intention of immigrating, she'll never adjust status. It's never advisable to enter the U.S. on a tourist visa with the intent of immigrating. http://www.dixonimmigration.com/index.php?pid=2
If a person enters the U.S. with a visa under K-1 status, they are entering the U.S. legally as a nonimmigrant. This status may be granted to them by the U.S. Department of State (DOS) after the petition their fiancé(e) filed for them is approved by the USCIS. After their legal entry, they may then be eligible to file for a work permit. This work permit will be valid for the duration of their visa, which will be 90 days. They may become eligible to extend their work permit if they marry your fiancé(e) within the 90 days and immediately file the appropriate application.
Failure to depart the United States on time will result in being out of status. Under U.S. law, visas of individuals who are out of status are automatically voided (Section 222(g) of the Immigration and Nationality Act).  Any multiple entry visa that was voided due to being out of status will not be valid for future entries into the United States. 
Every country processes visa applications at a different rate. Make sure to check the government website of the country you intend to visit to find out how fast they process visa applications. For example, visa applications from Russia to visit Canada take approximately 8 days to process, while Canadians looking to travel to India are advised to submit visa applications at least 15 days in advance.
H-1B temporary workers in specialty occupations and distinguished fashion models: Depends on the validity period of the labor condition application and the proposed period of employment, plus a period of up to ten days before the validity period of the H-1B petition begins and ten days after it ends. Most H-1B workers are initially granted up to a three-year stay. Extensions are allowed up to a maximum total stay of six years (with exceptions, notably for persons who are seeking permanent residence through the job). After getting your H-1B, any time you spend outside the U.S. is added on to and extends your three years.
The Visa Waiver Program allows nationals of nations that are part of the Western Hemisphere Travel Initiative to enter the U.S. port of entry without a visa. The Visa Waiver Program paperwork is handed out on the transport to be completed by each eligible person; if security checks at the U.S. port of entry do not flag the traveler for any reason, entry is typically granted for a period not to exceed 90 days. Entry is granted on several strict conditions, the two most important of which are that the traveler has in their possession a return trip ticket to their country of origin or another country outside U.S. territory, and that the traveler will not seek or perform work, either paid or unpaid.
Many countries have visa policies and agreements that allow their citizens to travel freely between them without the need for a visa. For example, Canadians and Americans do not need visas in order to travel to each other’s countries, only valid travel documents. However, Canadians do need visas to travel to Bhutan, for example, since no visa agreement exists between the two nations.
An incoming passenger can import up to two pets at one time. These include all domestic animals such as dogs, birds, cats etc., subject to producing the required health certificate from their country of origin. Pets are still liable for the usual quarantine checks upon arrival. Pets must also be microchipped with an ISO 11784/11785 pet microchip before arrival in India.
Each country has its own visa application requirements. Make sure to check with your destination country’s appropriate government website to find out. Requirements typically include filling out the visa application form, providing your passport for stamping if required, a photograph, and additional documents such as your flight itinerary, hotel booking or letter of invitation.
Some types of visa like B1 may not expire with the expiry of the holder's passport. An unexpired, endorsed visa in an expired passport may be presented for entry into the USA, as long as the visa itself has not been cancelled, is undamaged, is less than 10 years old and is presented with a valid non-expired passport, provided that both passports are for the same nationality. 

H-2B temporary skilled and unskilled workers: Depends on the labor certification and the proposed period of employment, plus a period of up to ten days before the validity period of the H-2B petition begins and ten days after it ends. Initial maximum of 12 months, with extensions of up to a year possible, limited by an overall maximum of three years.

^ Roberts, Jeff John (12 September 2016). "Homeland Security Plans to Expand Fingerprint and Eye Scanning at Borders". Fortune. Fortune Media IP Limited. Retrieved 24 April 2019. Unlike with documents, it’s very hard for a traveler to present a forged copy of a fingerprint or iris. That’s why the U.S. Department of Homeland Security plans to vastly expand the amount of biometric data it collects at the borders. According to Passcode, a new program will ramp up a process to scan fingers and eyes in order to stop people entering and exiting the country on someone else’s passport.
In general, to obtain a visa it will take four business days. To get a visa in 2-3 business days you can apply for the Express Service (it costs an additional 20 USD); while to get a visa within one business day you can apply for Rush Service (which costs an additional 30 USD). Note that the Rush Service is granted only in documented cases of extreme urgency. 
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