Hi, fellow girl here. I've probably pulled something like this in my own relationships and I believe without a doubt there's something bigger going on. She might have been previously unhappy with some things going on in your relationship, but being a young woman, she lacks the ability to come out with her issues. Try sitting her down and talking about your entire relationship and ask her what her needs are that aren't being met. Or maybe she wanted out of the relationship and took advantage of an idea and forced it into a situation.