How can I get my mom to stop spending so much?

My mom loves to shop at re-sale shops and thrift stores, and she finds really neat stuff. But recently I have noticed that the prices have gone up, even at thrift stores! And my mom still buys lots of stuff, and spends $60+ every time she shops, and its killing the pay check my dad works hard all day for, that is supposed to go towards bills and food. My dad has talked to her about cutting back on spending, but she still takes off when he isn't home to go shop. Is there anyway I can tell her she needs to stop without her getting angry? Any time I have hinted to stop spending so much she gets really angry, and says things like 'You just don't appreciate what I buy you!' and such. Please help!