My mom takes advantage of me and it hurts

My mom has always taken advantage of me. I am oldest of 4 siblings. Today I wanted to visit my family and relax. So I promised her I was going to buy Manny (age6) 3 school shirts. She ends up buying all my baby clothing and especially herself. I told her to take it easy on the shopping. The cart is full and I'm blinded by things she hiding in the kart. When I'm cashing out. She spots a dress that has no price that turn out to be a little out of my budget. So in price check it didn't had a price and a lady brings a blue dress which she feel in love with and said to bring cash out that dress as well so I'm paying for both dresses! I told her no! But she like I want that dress! When I cashed out the total was $200 dollars. Which I was going to put away toward my baby savings since I'm pregnant and trying to save money. She tricked me. I told her to leave some stuff behind and she got mad. She so ungreatful and it breaks my heart. Every time I fall for it cause I love her and want to see my siblings. But I think this is pushing me farther away. It's sicken me. The cashier lady was even sicken by mom mom attitude. I suffer from bad stokhlem syndrome.