Mil told my daughter that she can't eat the food she buy...

Mil will tell my daughter that she can't eat because your mother say you can't eat. She will eat in front of my daughter and say that. My daughter just sit there watching h her eating and can't eat. My daughter is 5yo this year. Seriously i am not aware of this until yesterday!!! I think she been saying the for very long because I heard she say (.... Can't your mother say can't, not Idw to give you is your mother say can't.) . Idw to ask my daughter cause she is just a kids. It really hurt me when I found out she buy the food my daughter can't eat and yet she eat in front of her. Can anyone advise how can I make it up for my daughter? How can I talk or do anything to make my daughter little feelings better?