What is the ruling on a man having intercourse with his wife after she has performed ghusl following menstruation, but has only washed her body and not her hair due to a "hairdryer/styling," and what is the expiation for such an act?

Washing the head is obligatory for ghusl (ritual bath) after menstruation and janabah (state of ritual impurity requiring ghusl), and merely wiping it is not sufficient. A woman must fear Allah in matters of purity; otherwise, she would be required to repeat the ghusl and the prayer. If two reasons necessitating ghusl combine, such as menstruation and janabah, and the woman intends one of them, it suffices for the other according to some scholars, and this is the more correct opinion.