Giving a 5 month old soda

So tonight my mil was holding my daughter and she was drinking Pepsi well I look away for a second and look back to see her giving my 5 MONTH OLD daughter soda. So I jumped up and took her out of her hands. Well then shI gets mad gets up and starts crying and walks away. She already knew we don’t give her anything except baby food and breast milk. Am I wrong for getting mad and taking her out of her hands?