They are treating you like a child, I'd be upset also! Your mom is right that it is her house, but it is your business, and not hers...I'd be the perfect balance of curt and polite to the awful woman, and not tell your mom anything you don't want her to find out...don't throw tantrums, that will only make them think they are right to treat you like this. I am living by "be the bigger person", believe me I know it is hard, but you will then have nothing to regret, and your child will see it for what it is someday.