MIL ruined my breast milk

I'm literally so pissed right now but at the same time I just feel like crying. I was out of state for 3 weeks with my fiance for a family emergency. Our house lost power and my mother in law went to stay with a friend. My fiance specifically told her to grab my frozen breast milk and put it in her friend's freezer. She didn't feel like getting it, so 40-50 ounces of my milk went bad. I'm so mad right now but all I can do is cry because I worked so hard for it. It especially sucks because while I was out of state with my fiance I had to do a lot of driving on a time limit (long story) and I was forced to give her formula to the point that my supply dropped so low and I am unable to breastfeed anymore, so I was hoping I could still give her as much liquid gold as possible but now I have none for her. I guess rant over