Most Helpful Girl
I get what you're saying, she sounds like an easy girl and you def don't want that type of relationship, because then you'll always have that self doubt about her ability to stay loyal without flirting around with other guys. So acknowledge the fact that she is going to be at this party, so be nice smile at her and say hello but then move away. If she starts grinding on other people or dancing around look at her and realize that that's not the type of girl that you want.
It's easy to fall in "love" or like someone because they can be exciting and new but like you said, that thing she told you really bothered you and so rest at ease with knowing that she's not the type of girl you should hang out with. Warn your buddy, let him know that as his friend you would suggest not hanging around too much with her or getting attached.
At the party have a good time but after your dues take the time to chat with your friends and shake loose (responsibly). lol