What should I do now

I have sole physical custody and joint legal custody of my 3 yr old daughter. Mom walked out when she was 11 months. In my divorce, i gave her joint legal custody so she would not fight the divorce.

She hasn’t paid one penny of her court ordered child support and hasn’t seen, emailed, written, or called her daughter since Halloween. Is there some way i can get sole legal custody too and arrange if something happens to me my mom, who stays with me now to help me raise her, gets custody?