how can i get my mother to stop spoiling my daughter

when my daughter wants something she sees in the store or on t.v. and i tell her no, my mom will buy it for her. it doesn't happen all the time, but enough times for my daughter to say "grandma will get it" when i say no to her. i have asked my mom multiple times not to, but she continues to do so. maybe i'm not asking in the right way?