Your daughter has the right to ensure that her ex does not continue to state that he caught an STD from her. The allegation is untrue and accordingly is actionable in defamation. She can raise court proceedings for defamation and damages for injury to feelings and any financial loss. She can also ask the court to grant an order stopping him from making the allegations. Those are the remedies and before court proceedings are raised a cease and desist letter could be issues. Note that legal aid is not available for defamation proceedings and that any court action would have to be funded privately although you would seek costs from the ex. Happy to discuss. I hope that helps. Please leave a positive rating so that I am credited for my time.