What Does Relapse After A Coma Signify?

HRelapse after a Coma? What does it signify?
My friend (20,female,non heavy smoker nor drinker) had a car accident back in February. She got a bad cut on her neck and was though that could have memory loss. She was under a medically induced coma for about 2 months and a half. They had problems waking her up one time but the next and final time, she woke up by herself. She did have some memory loss but nothing very severe and her neck healed great and she was kept in the hospital for observation and tests for the following month. Though I believe they must have gone a bit too crazy with the drugs while she was there, she got out and everything was running fine with her.

Now about 2 months have passed and she just had a 'relapse'? She went to sleep and has problems waking up.Doctors said: Her coma had done a lot of damage and I guess it just became too much for her body again.It started with bad headaches, restlessness and a lot of sleeping. She slept more than she normally did.

PLEASE tell me more about this! How long could it take? Common? Cause? Possible Outcomes?

THANK YOU!