Is your fianceé a Nigerian? If yes, you should be looking at the US embassy website in Nigeria to get all the information you need about the visit.
She will need to get a US visa. The application form has to be filled and submitted online via https://ceac.state.gov/ceac/ And she will need to create an account to book an appointment for her interview. All necessary links for Nigerians will be found here: http://cdn.ustraveldocs.com/ng Wishing both of you success.
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