Sadly, I've seen this happen to my friends before and I feel like when it gets to this point, there are only two things you can do:
1. Go with the above suggestion and talk to her nicely about possibly seeing a therapist and the value of learning to appreciate yourself, or
2. Let the friendship go. It is harsh and difficult, I know, but someone like that is just going to drag you down and wear on your nerves. It is like the old saying goes, "if you want to be successful, hang out with successful people."
As you mentioned, there's a big difference between trying to help a friend in a time of need and having your advice fall on deaf ears. I've been happier easing myself out of destructive friendships than if I had held on, I know it.