abhagi kale,

Your niece need to do certificate validation with CGFNS or some other organization in US first. Then, she has to apply for particular board of nursing in USA. Ofcourse, she either need to take NCLEX for license or CGFNS exam.

For details, your niece can communicate with the National Council of  State Board of  Nursing.

Here's the website: www.ncsbn.org

Good luck!