A catfish is when someone uses a fake identity online to catch someone cheating usually. For example, if a wife thinks her husband is trying to cheat on her using a dating site, she would make a fake profile and catfish him to prove it. There's an MTV show about it.
The urban distionary defines a Catfish A catfish is someone who pretends to be someone they're not using Facebook or other social media to create false identities, particularly to pursue deceptive online romances.
Someone who is using someone else's picture. Whether it be off a website or the Internet. She probably thinks you have used someone else's picture. Pretending to be someone your not, which yes can be applied to being fake.