It's in the best interest of everyone, most especially the abused woman who has abusive tendencies, to seek counseling for herself. She should also stay out of relationships until she has adressed why she is abusive to others. Getting involved too soon would be a rebound relationship.
Even if her ex was willing to take her back (and he might not be), it's unhealthy to jump from one relationship to another in hopes of being saved from a bad situation, or believing all personal problems will end if they get with someone who once had feelings for them. The abused/abusive person must heal themselves first before they enter a new relationship.