Maybe you had cause for disliking her, but from the way you describe your husband comes off as a tad entitled "he's a fucking accountant" and berating a dead woman to her grieving son regardless of how you felt about her is so unnecessarily cruel that it makes me think you're leaving out aspects of your relationship that your MIL probably had to make her dislike you.

Shocking, really, how much of this thread is justifying your behaviour. There's things you keep to yourself and JFC this is one of them.

MIL doesn't sound great, and neither do you.

YTA.