This is an antiquated practice that many are trying to end. It is used as a way to control women in many cultures.
www.fgmnetwork.org
Please get your friend to a doctor immediately and reiterating what some have already said, if she's under 18, her parents should be jailed for abuse.
Here's an excellent article explaining the process, laws and the lifelong harm on women who are brutalized in this fashion:
http://www.parkridgecenter.org/Page131.html