A husband has no authority to stop his wife from
covering her head. He cannot overrule the directives of the Almighty.
As far as the second part of the question is concerned, a
woman can seek divorce from her husband on these grounds if she can bear the
consequences of such a divorce. Allah will definitely reward her for this.
However, she must be very realistic in this regard. Facing the consequences of
divorce is not easy at all in this society. If she thinks that this would be
too much for her, then, of course, she has a genuine excuse to continue with
her husband. She must know that Allah never requires of a person something
which is not in his or her control and always entertains legitimate pleas.