Please answer:) How can I talk to her about flirting ?

Okay so theres a girl in my grade, Tabitha. I'm a girl too. Tab is in our group of friends all of a sudden and I really don't like her. Im having an end of the year party and I felt obligated to invite her because then shed find out (I also didn't harbor as much as a hatred for her when I was sending invites). So dont tell me I shouldn't have invited her or whatever. She's a huge flirt- especially over the guy I like. Pool party? Bikinis and shirtless crush. But I don't want to be as flirty as she is and be all hangy, possessive, and competitive with her all throughout MY party. I've talked to him about her and he said they're "sort of friends". So he and I are closer but he's very personable and it's not like hes just going to ignore her when she talk to him. But the thing is that I actually want to have a relationship with him (hopefully) in the future, so I'm not going to stoop to her level and spend my whole party combatting her. Grrrrr. So I need ideas on how to block this. I was thinking of trying to buddy up to her and her I like him but I think shed either a) tell him or b) innocently flirt with him more. She wants attention and is immature. We had a case in the past where my friend confided her crush in her and she told everyone, including him. But then I also thought that it could work to my advantage if she told him because if he liked me then he'd ask me out. So thanks if youve taken the time to consider this. It's quite the mine field. Suggestions are what I'm looking for. :)