ANSWER:
She must take medical reports from the hospital proving such domestic violence. With such reports, she must warn him that she will call the police if he ever physically abuses her. She should involve her father and brothers to let him know that there are men protecting her and ready to beat him up if he thinks he is strong!
Being in such an abusive marriage is not healthy as he might permanently damage her if not kill her one day. He needs to know his limits.