My boyfriends mom has helped us with our baby a lot and I appreciate what she’s done but I’m feeling EXTREMELY disrespected and I’m not sure how I should handle it.

We dropped our baby off with her to go get some stuff done. My baby is a breast fed baby and has never had formula. Well while we were gone she took it along herself to give my child formula without telling me. After we had picked up our baby she was spitting up different color than normal and my boyfriend had asked her about it and she said it was just mucus that she was spitting up still failing to mention that she gave my baby formula. We later end up taking the baby to the hospital and on the way there she mentions that she fed her formula. Not even to us but to his sister which then tells us. When we call and ask her why she would even do that she couldn’t give any answer. Then she only apologized to my boyfriend about. She bows how hard I’ve worked to breast fed our daughter and she just gave her formula without either of our consent. Then she was talking behind my back to his sister, which she also told us. My baby had 3 servings of pumped milk with her and I wasn’t gone for more than 1 and came back when it would have been time for the 2nd. I called and kept asking why she would do that when I first found out and then i ending up hanging up do to lack of answers. I don’t know how to handle this situation.

Sorry for the rant but opinions would be helpful.

update:

We have no problem with formula but I have allergies to many things and we made our choice because she may have those same allergies. My baby is only 8 weeks old, with her still being this young the concern for an allergic reaction is great for us. Which the hospital said that she was vomiting due to an intolerance of the formula. We found out that his mother fed her formula because she “wanted to try it” despite knowing the concern for allergies we had. Then changed her story to “ The baby is underweight”. Even though my child just had a well-child visit last Friday and is in perfect health, she was 7lb 10oz when she was born and dropped down to 6lb 13oz by her first appointment. She is now 9lb 5oz. Which is mother knew that there had been no concern for her weight after her 2 week check up when she was back to birth weight. She had bought the formula when I was still pregnant even though it was clear from the beginning that I was going to breastfeed. After arguing with his entire family on the fact that we choose to breastfeed our child because they feel she is not getting what she needs from it. We have decided that we are not going to allow them to see our child until they can respect that decision. We have not spoke with any of them about our decision as we feel we don’t have to explain ourselves when it comes to our child.