What can I do if my child's grandmother is abusing her?

Ok so my 4 year old daughter has a very weak tummy alot of stuff makes her gag and sometimes puke. Her grandmother on fathers side found out about her weak tummy so now everytime she sees her or we visit she puts relish on her finger pretends its boogers and wipes it on her face or take a pinch of cheese and says it is her foot skin than puts it in her mouth and everytime she does it she never says sorry just laughs in her face and after she gets out of the bathroom and says im just kidding. She does other abusive things to her other grandchildren but I am worried about my own. And was wondering what I can do about this? And I am in mass