MIL Vent!

My MIL has been watching my girl during my first week of work. I give her tons of frozen breast milk to give her, but she took it upon herself to buy formula anyway "just in case". We supplement sometimes in the evening and she knows that so she thought it would be ok. She's already given her some and it's only the first week. I'm frustrated because I'm struggling with my supply as it is, so I've been explaining to her that when she gets a ton of calories during the day from formula, it signals to my body that she doesn't need it from me. Fast forward to today and she took her to work with her and left the breast milk at home. So she's only getting formula today. I'm so frustrated. I know my baby will be fine and healthy and that's what's most important, but she is ignoring my needs and what I want from her. It's hard enough being away from her, but now I feel like I'm completely out of control of her care. I know I'm overreacting because I'm emotional about leaving her, but I just feel so helpless. Anyone else deal with family members not listening to their wishes?