If this girl asks me out again, what should I say?

Ok, there's this girl who goes to my school, quite fit, nice personality, all that. I get in my first ever relationship in my whole life with her for 6 months, after that she breaks it off, long story short I was heartbroken. Then she goes out with another guy straight after, and another one, none which lasted as long as me though. During that time we became quite good friends again, healed old wounds etc. But after her last break-up I felt quite appaled, because the guy she broke it with is actually a good mate of mine. It's not like he was acting like a jerk, he just didn't know how to deal with a relationship, so all he wanted to do was keep his distance, which is fair enough, because I know as a girlfriend she demands a lot of attention, fairly high maintenance. She was just bitching and bitching to me about him, and she was bitching to her mates on facebook too. I could see justification in both sides, but all the time I felt I was being used as some sort of pion, she wanted me to talk to him about being a better boyfriend, he wanted me to talk to her about being a less demanding girlfriend. To be honest, I just wanted out. But now I think she's trying to ignite old fires, she always wants me to be on her side. I think of the beautiful relationship we had together, as first relationships go that one was actually pretty awesome. But I also think of the girl she has become, not the sweet, modest one who I could relate to. Now she is expecting hugs and support out of me, and we're gonna see a movie with a mate at the weekend. I'm fearing a lot that she'll make her move again. I maybe acting irrationally but she is that sort of person. I don't know whether to trust my forgiving and tolerant side or my sensible side. Please help me :(