Just because she has been with a lot of people does not mean that she will seek out someone's boyfriend. She may love sex and see it as a game, but that doesn't mean she has no morals. Unless you know that she can't "control" herself, I don't see why that should even figure into her being offered a bid. You can't tell me that all of your sisters are totally "pure"!
However, if she prides herself on getting other people's guys, give her the BOOT!