It's too late, I'm writing a Fred Weasley fic.

It starts in The Goblet of Fire. The oc is Cedric's twin and the face claim is Maia Mitchell. She vegans talking to the twins when she sees them preparing for a prank they were pulling on a Slytherin. She told them how to make the prank better, and since then she's stuck by their side. Not realizing she was falling in love with one of them.