The following are pretty much only the following ways your friend could move/immigrate to the US:
Marry an American citizen or green card holder (permanent resident). Requires affidavid of support from someone in the US.
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.
Get a transfer within the UN (G visa) or within another company where she has been working for at least one year (L visa).
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
For most people the only ways to move to the US are the same: marriage, work transfer, sponsoring by a company or winning the green card lottery. There are also investment visas, but I have heard rumors that due to mis-use of them, they may go away soon. On top of that you have a number of much more specialized visa types, for artists, professors, au-pair, etc. But for most I woudl say that the ones listed above are the ones available.