[Face Up.]

I'd sit her down on a day when she's in a decent mood in an area where there aren't any distractions. If you can't meet her in person, do it over a phone call instead of texting.

Let her know that you appreciate the fact she wants to have sex with you and you understand that it would take the relationship to the next level. Let her know that you are okay with having sex, but that you want to be sure that your relationship won't be only about sex from now on. Let her know that you really like her and want to spend time with her outside of having sex as well, and explain some things you would like to do with her that can show your love (ie cooking a meal together, having a movie/game night, or something else). Hopefully she will be on board and feel the same way!