Unless there is some serious malpractice going on (which could be possible; we don’t have enough details to do more than speculate) I think the situation is being blown way out of proportion. Okay, so there was a misdiagnosis, and rumors spread, etc etc and it’s hard to repair the damage. But those who really matter won’t listen to rumors and will appreciate your friend for who she is– and, furthermore, wouldn’t care even if she did have Asperger’s. I have a few close friends with Asperger’s and they’re wonderful people, and function quite well (just differently).
Making diagnoses, especially those related to mental rather than physical health, is not easy. There is a lot of “gray area” and it’s not always clear (that’s why autism is called a “spectrum”, because people present in different ways). Furthermore, especially as a youth, one can present symptoms and then have them disappear. What does that mean? Did the person really have the disorder and then it went away, or did she never really have it to begin with? It’s hard to say. Science has not advanced enough to the degree of precision that we would like, and that’s difficult to accept, but it’s true.
I would suggest to you and your friend that you stop looking for scapegoats and focus on moving forward in a positive way. Much hatzlacha.