I agree with the others that you should find out what the time limit is to return it, and then find some other reason to go to the mall area. As another poster mentioned, this machine is kinda pointless for your purposes anyway. Do you think you might even be able to get cash back with receipt? If they make you take store credit, you can probably find something much more useful for the amount of money anyway.
I'm really interested in if you plan to express your displeasure (nicely!)/already have, and tell her that the gift defeats the purpose. I am wondering because my MIL is pretty famous for doing this same thing, every year for every gift recipient. No matter what is asked for, and no matter how specific you are about WHY you want a particular item or model, she will always "splurge" to "treat you" to a perceived deluxe model of the same thing. (I once asked for a single sauce pan in a particular color - making it very clear that I wanted to develop a collection of pans that were each a different color -- and she bought me a $500 set of pan sizes I will NEVER use, all in a single color, from an online retailer that did not accept returns after 14 days.) No one has figured out the right thing to say to stop her, or even get it to sink in that she's making no one happy by doing this and is wasting her money.