My son has sole custodial of his son.His sons mother has supervised vists cout she does not come all the time and she doesn't call the day she will not be coming. Some time she does not come for months at a time.Can my son take her rights away.

No, your son can't take away parental rights. Only a court can and Courts rarely will terminate a parents rights. You might find this sticky helpful:

https://www.askmehelpdesk.com/family-law/signing-over-rights-read-first-116098.html