C.E.
L. I am sorry this happened to your grandson. You said the bit broke the skin? No matter what the first thing with any dog bite is to clean it out! If this woman didn't you may have some prblems in the next few days. Once you take him to the doctor, they will file the paperwork and report it to the police/animal control. Any dog bits require proof of rabies certificate being up to date. Even if it is your own dog. In the event it is your own the doctor pretty much puts the paperwork in the file.
had a friend of mine get bit by her own dog, and when she realized it was the one who got missed, she had to produce papers on everyone to the city.
Also from the sounds of this, if you take him to the doctor, which I recommend, you then have proof he was injured while with her and you more reason to not let him go back if she gets nasty about it.
Good luck have it checked just because and let animal control handle it.
Chel E