AU.  Pre-canon (I'm thinking back when Charity had her magic stage, but I don't know Harry and Charity's relative ages, so it might not work that way), Charity and Harry met and became friends and stayed that way until they lost contact.  Fast-forward to Harry being introduced as Michael's friend the wizard.  Charity has mixed feelings towards him, but she's nicer than in canon--he might be a wizard, but he's Harry.