What should sleepover rules be for my bisexual teenage daughter?

She is 13, and came out as bisexual to me (and Facebook) this spring. As a single father, I am wondering what the sleepover rules should be. I don't want to forbid them outright--not all female friends who come for sleepovers would be potential romantic partners, but at the same time I know there is no way I'd let a boy sleep over with her--platonic or not. And I don't want to grill her about girlfriend vs. friend every time she wants to have a friend spend the night.