am I overreacting?

Erin • Mama to 3 beautiful girls
I let my 4 year old have a sleepover at my mom and dads house on Saturday. I told them weeks ago that we have changed our diet to a pretty healthy one for the sake of our 4 year old who has tummy problems. 
I told them what we hadn't been giving her, which included sugar, like candy. 
Well today, my daughter tells us that "grandpa gave her a soda in a bottle" while they watched a movie. I know that the only soda "in a bottle" they have is coke. They gave my 4 year old a Coke. I don't even drink Coke. I don't drink soda. We don't have soda at our house. They know that. 
 I texted my mom at noon today and still haven't heard back from her.