I met a girl a while ago at a party, shes a HB8, I simply used some negs etc. we made out that time and a couple of weekends at parties after that. Although one day I got really wasted and got pulled away by another girl (which turned out to be a psycho or smth) and left with her, and the HB8 got really mad at me. She even called me that night and said "screw that girl, come here now I really want you", but I was just stuck with the other girl. I tried to say sorry the next day and I know I should have took her out somewhere but I was really sick and couldn't move out of bed for the next few days - I was totally fucked there.

So pretty much that ended all conversation, but one weekend she came out with us again on a concert, although I ignored her because I was drunk and really afraid to talk to her so I don't fuck up even more, basically we didn't talk to each other the entire night even though we were in the same circle of friends for that night. (note that night was my birthday, she didn't even say happy birthday or didn't want to drink stuff that I brought and my friends offered to her. Although I did catch her 4-5 times glympsing at me and checking me out, she was clearly expecting me to do something but yeah..)

Now I'm having a small party and I really want to invite her, but have no clue what to say or what to do because we ended on such bad terms. The only option I see is inviting my mate's sister who's friends with the hb8 so hopefully she'll bring her somehow..

Any advice?

So you've blown her off twice now --- once for another girl --- and you think she's going to be down for your party?

Who knows, maybe she will.

Do you have her phone number? FB?

I'd hit her up beforehand and chat a bit... Make sure she knows you want her there.