Do you want an actual relationship with this girl or mostly just want to ultimately have sex? Just take plenty of time and do lots of foreplay and petting. It sounds like you're both young, and even if she's not a virgin, she's probably not yet a great expert on sex or her own sexual response. Try not to set yourself up by setting expectations for what should and shouldn't happen. It ought to be spontaneous and fun. If you do end up having sex, make sure you wear a condom, but don't expect her to have an orgasm through intercourse. That is generally not the way it works for women.