Well, if she's really a friend, and not "a piece waiting to happen," then I'd say you didn't waste your time/evening.
Lemme guess; she had some traumatic event happen in her life that absolutely required you to sit there and hold her hand/listen to her whine (ie. fight with her sister/cat died/argument w/her coworker/man troubles)
Women whine like that and by you sitting there all night and being her friend, you did a very good thing.
Real
friends, not aquaintences are almost as important as family. I have a few female "friends" (i.e. no sex) myself and they've helped me out more often than my male friends have. :|
You did the right thing...I think...you didn't exactly give a lot of info.