She's 16. What did you expect? Not trying to be mean, but really, you've been through high school (I'd hope so, at least), you've seen how quickly relationships end in that age group and how quickly new ones start. I'm sure you've seen how loveless they are. To answer, leave her be, avoid her, blah blah like everyone else said. If she tries to keep something up by talking to you, tell her to bugger off.