I suggest you get her to a psychiatrist, but how is a different issue. You should stick to what you see directly when you are with her about this pattern, and use that as the reason she should get help. The other may be too explosive, but that is judgement call you have to make , and it may be necessary.
It does sound like a serious personality disorder. Good luck with helping your friend. I hope and pray that after you talk to her she will be willing to get some help. What's sick is that the guy who calls her a friend takes advantage of her illness in order to get his sexual jollies. I would be trying to put a stop to that right now. Again, Good luck and I commend you on whating to help your friend.
Jimmy
Sounds like split personalities. It suggests that something(traumatizing) happened in her (early)life that she is blocking. You should try and convince her there is something wrong, but if she refuses to believe it, theres nothing you can do. She will eventually hit a bottom. You have to decipher whether or not your willing to take this ride. Good luck!
Without going into anything she may or may not have done during these "blackouts," I would encourage her to see a physician simply along the lines that you're worried about her bouts of amnesia. I would not assume that this is totally a psychiatric disorder unless she is medically cleared first. It is possible that she has some form of seizure disorder that is causing these incidents (seizures can be set off by physical or emotional stress in some people with seizure disorders). Not all seizures involve falling down and losing consciousness; there are other types as well. At any rate, it certainly does seem like she would benefit from seeing a doctor.