[Kiddiss]

It sounds like your friend may have a few issues going on.
In addition to everything Fey said, there may be a few things to point out to your friend.
-> If she is actually doing this (or convinced herself she is doing this) to understand how starving children in Africa feel, point out to her that by doing a fast, she's not helping those kids at all. If she wants to help famine victims, she can donate money (if she has a job), or her time to a group that has a proven track record of helping people. The reason I say "proven" is because too many charities have been found to misuse monies that were supposed to go to a specific cause.

-> Also, if she is a teenager or early 20's, a fast can really hurt her normal growth. Many people think you stop growing when your teens are over, but I know from my own body that growth can continue through your early 20's (my body didn't stop developing until I was 23).

-> Just because someone else says they fasted for a month and a half is no reason to try it yourself. I hate to use the old, "If your friends blindly jumped off a cliff" B.S. that parents resort to, but peer pressure is often a factor in what can be considered a radical action (and, yes, I believe that fasting for a month is extremely radical). It's even worse if your friend has body image issues.

If you can't talk her out of it, is there someone whom she looks up to, like a role model in her life, who can sit her down and talk with (not to) her about this?

I wish you the best of luck. The fact that you have even posted this question shows that you do care for your friend.