William can do what he likes, but she lives in America (his law and edicts can’t touch her) and even if he strips the title she can and will use it. Even if she divorces Harry, she will use it. She doesn’t care and he can’t touch her.
William should absolutely remove Harry and his kids from the line of succession. That is much more important.
And IF she ever ran for ANY political office, in America, she WOULD have to relinquish any/all titles!
Actually, they can. Strip the title and sue her if she uses it. English law is clear, but she is also using it for business and financial gain. They could sue her right back into reruns. An American judge would stay her use of the title for years as the civil case runs through the court. She is already damaged goods, and only wannabe famous people bend the knee to her. Actual famous and powerful people want nothing to do with her and by default her pet Harry.