Is this marriage valid from the start, and would the girl be considered disobedient to her parents if she sought a divorce from an abusive husband, despite her parents forcing her to stay with him?

The husband's mistreatment, beating, and humiliation of his wife is an ugly act. Her family should sit with him or his family and discuss the situation to rectify it and do justice to the wife. If the husband does not hold on to her with kindness, then he should part with her in a good manner. Neither her mother nor anyone else has the right to compel her to stay with him in this condition, for the wronged wife has the right to seek divorce. She is not obligated to obey her parents in matters that cause her harm, and in this case, she is not considered disobedient.