locked out of bellsouth/att/yahoo mail account

My 80 year old mother has been locked out of her email account.  Her password does not work and her security answers are not valid. It is evident someone has hacked her email account and has changed her security settings.  All the advice thus far has been to reset her password, but if she can't access her account she can't reset her password.  How do we regain control of her account in this scenario?