Am I wrong here?

My 6 week old got an MRI and had to be sedated for it. The nurse told us when we were leaving to make sure to have a quiet, relaxing evening. My mother in law asked if she could take her for a walk. I decided reluctantly to let her take her thinking a walk wouldn't be too crazy. She then told me she was going to take her to her mother's house after we had already told her about what the nurse said. Turns out instead she took her to a community band concert in our village park, never told me she changed her mind and went there instead. Never even told me after the fact. I'm livid about it. She lied about where she was taking my daughter whether purposely because she knew I wouldn't be ok with it or by omission. Worse part, she did tell my husband after the fact and HE didn't even tell me knowing I wouldn't be happy. Someone else told me on Facebook that they got to meet her at the band concert. And my husband is defending his mother, he doesn't see anything wrong with her taking our daughter somewhere other than where she told us she was taking her. And he's upset with me because I'm upset with her. Am I wrong to be upset about it? Am I overreacting?