1. Here's the deal, you don't have any business regulating your daughter's sexual activities. She is an adult not a child. If you raised her right she should be able to tell a good judgement from a bad one. If she can't do that then you're part of the problem and not the solution.

2. What difference does it matter if she has sex with this girl? She probably already did anyway. How is it a problem? She's not gonna catch aids is she?

3. Let her know that she can do what she wants as long as she's safe. If she's having unprotected sex or doing intravenous drugs with gay men then you won't support her or allow it. Simple.