S.C.
Wow. I feel for you. I have to say that I think this is definitely not the norm for seven year olds. One piece of advice that I got that I always take is when there is a drastic switch in behavior, no matter how innocuous, check in with a psychotherapist. Just so you can be equipped with the right questions to ask and also to allow yourself to feel better that nothing horrible has happened to cause a shift in behavior. If you dont know of a therapist, talk to your pediatrician or talk to the school counselor.
The next thing is to really look at what may be influencing her. Is she watching Hannah Montanna, High School Musical, Disnesy's Barbie movies? I'm not against those movies, but I limit exposure. AND when my kids do watch that stuff, I'm right there with them explaining that Troy and Gabriella are in HIGH SCHOOL. They are much older. Barbie princess is ready to get married and have kids when she meets the prince. When they show little barbie she isnt kissing boys. I point those things out to them. (Part of the problem is little barbie acts babyish like a toddler. And adult barbie acts like a preteen all the way up until the kiss. guess who they identify with.)
Kids model behavior and there's not much stuff out there for girls her age.
My twins are just turned eight, and my daughter has other young girlfriends who have mentioned they are in Love with her brother and that he's their boyfriend. I've made it clear that at their age, boyfriend and girlfriend does NOT mean kissing. Thankfully, my son agrees Kissing girls is yucky.