Revenge. First, go to this girl who according to you is pretending to be lgbtq for attention. Get closer to this girl, until she can tell you who her crush is. Then shortly after, tell her that you're ace. She'll more than likely follow in your false steps, she'll pretend to be ace. Inform her crush about it, now she wont get whoever she likes, and if she does tell it'll be terribly awkward. That'll teach her a lesson.