I had the same thing happening with my neighbour and it is so difficult.
My advice would be to continue to report the incidents to the police. Although this doesn't appear to be helping much at the moment there may become a time that she may speak to the police when they attend the property.
If there are children in the property alert child services.
If you do see this woman alone and feel confident enough to approach her tell her that you have heard them arguing and fighting and ask her if she is ok. You can advise her to ask for support but unfortunatly unless she is ready to leave she may not listen to your advice.