Mom: By the way, I talked to a couple of people I know in HR: they said you are an idiot, you shouldn't have written it so-and-so but this-way-and-that.
This is far from the first time she snaps at me and calls me stupid after I made a mistake: in fact, she has been doing it for as long as I can remember.
(And yes, I realize that maybe she's just repeating what the HR people said, but did she have to? I mean, if somebody did call your child stupid, would you go and tell him/her?)
Please stop and think. Do you genuinely think the people in the HR department said to her, "Your child is an idiot"? I sincerely doubt that this is at all the case.
Which of course leaves us with the most hurtful slant on this, which is that your mother is the one who is calling you an idiot.
I lost my mom just a year ago, and I am occasionally bereft because she was the ONLY person that I truly believed would love me no matter what I did, no matter how awful or irresponsible or mean. And she she was clear-eyed and direct enough to never IGNORE my awfulnesses--she wouldn't kid herself about me and my mess-ups, but she would love me anyway.
I want to cry, thinking that you don't have that.
Maybe you can push back in ways--maybe a straightforward conversation wouldn't help you much, with her.
But maybe you can say, "Mom, I sincerely doubt that the HR people were rude enough to call your child an idiot; are YOU calling me an idiot?"
Or just say, each time, "That hurt my feelings!" and leave the room.
Basically, you need to find some negative stimuli that you can give each time she does this.
And never get into the whole "what is wrong with you" bit--just say "Well, whatever, it still hurt my feelings. I'm sure you could pick kinder words if you wanted to."
In fact, if you want to try a "cut and paste" technique, that might be a phrase you can use over and over and over.
"I'm sure you could pick kinder words if you wanted to."
(edited to change "different words" to "kinder words")