MIL issues

Does anyone else have a MIL who's a habitual thief? Last night I came to the realization that my SO' s mom stole a casserole dish my mom gave me. It's not really about the damn dish, even though it's a $20 dish, but it's about the fact she sees nothing wrong with stealing from her own son's house and then tried to lie and say it was hers WHEN THE DISH STILL HAS MY NAME ON IT (and she was stupid enough to not at least try and remove it 😑) I don't even want her in my house anymore, before this she tried to run off with my damn makeup bag and phone charger by tucking them into her purse! Am I being ridiculous or do I have a valid reason for being slightly upset about this?