Yes, bring law enforcement into the situation.

Have an intervention. Before you do so, do some leg work on her behalf. Don't merely say you have to leave; instead, give her aleternative options. Where can she go for help? What shelters or homes are there she can go to? What resources exist to help her financially. It is vitally imperative that she know there is hope on the horizon. Simply telling her life will be better won't work unless you demonstrate that to her.

Offer her emotional support. Find out about bipolar or mood disorder support groups and offer to attend a meeting or two with her if these groups allow (my group encourages this).

Finally, you might want to investigate the laws where you are regarding grand parental rights. They just might be in your favour.