NTA. 100% NTA

Your husband could chalk it up to a "misunderstanding" if it had been the first time, but not the third fucking time.

This is classic toxic MIL syndrome: very passive-aggressive, pleading innocence, pleading good intentions... and stepping all over your turf.

I might ask: is she going to reimburse you for the cost of the groceries she wasted? Meat's expensive, and your MIL just chucked it away.

Did she bring her own groceries? If she did, then this was intentional. If she didn't bring her own ingredients, then she just used up more of your grocery bill without (I assume) contributing to the cost.

Tell your husband that he's married you, chosen you... but his mommy won't be cooking for him forever.