Thank you for your comment, BlueInanna. It makes a lot of sense, and it made me feel better.
I think you're right. I think a big part of it was a sense of injustice, and well as... perhaps 'perplexed' is a more fitting word in my case than confused (but I would think it translates to about the same) over someone first of all acting so entitled, and then for slandering my mother like that.
And I'm ok, thanks. Still annoyed, but I've mostly calmed down.