For all purposes there are pretty much only the following ways your friend could move/immigrate to the US:

1) Marry an American citizen or green card holder (permanent resident). Requires affidavid of support from someone in the US.

2) Get a company to sponsor a work visa, e.g. an H-1B. There are a limited number of them, most being used by Microsoft, Google and other big companies to import foreign engineers/programmers. These visas are time limited. They can be converted into green card/permanent residency if the employer sponsors that as well. Unless she is a very skilled worker with unique skills, this is unlikely.

3) Get a transfer within the UN (L visa)

4) Win the right to apply for a gren card in the diversity visa lottery (a.k.a. green card lottery). It should open again in October 2016.

There are of course a number of very specialized visas, you can find a good overview here:
https://en.wikipedia.org/wiki/Visa_policy_of_the_United_States#Classes_of_nonimmigrant_visas
About green card: https://www.uscis.gov/greencard