That's just horrible! And yeah, your mom's behavior is completely out of line. She should be supporting you throughout this, not cross-examining you.

I admit I'm not the best at advice, but I'd tell her that you definitely need to breathe a little and she doesn't need to cross-examine you. Probably as gently but firmly as you can. In the meantime, take care of yourself.

I hope that helps, at any rate. I'm not the best at giving advice.