My SO told me that a girl he works with flirts with him?

Last night my boyfriend came him and told me that he doesn't know what to do there is a girl at his work that constantly flirts with him. I told him he should say he has a girlfriend make it clear your not interested. He said he did and she told him she doesn't care. I know this girl we even were friends I told him to not talk to her and he says she leaves notes for him on his desk. It made me so mad at her that I contacted her on FB and she denied everything my SO was saying. I believe my SO he has no reason to lie what should I do?