Mother breastfed my baby

My mother was taking care of my 3 months old who was very fussy. I went to make formula milk meanwhile she said to my baby are you hungry and put her breast in her mouth and joked baby you won't get milk her. I definitely didnt like it and took her breast out and shouted please don't do this. Am I overreacting? When I again told her not to do this again ever she said you dont understand the joke. I dont like someone kiss my baby lips or do something like this be it my own mother. How do I draw that line? Its my baby and she loves her grand daughter but these kind of stuff make me angry. Am I wrong?