I am so fed up with the double standards afforded to one of my coworkers. What can I do about it?

I have worked as a courtesy clerk/cart pusher for over 3 years at this point, and I have never worked with anyone more frustrating than this one coworker. Almost all the other cart pushers hate her because she gets off free despite very rarely actually pushing any carts in. I normally work grocery side, and she's sometimes assigned there with me. Despite that, I basically have to work that side solo for eight hours. Now it's summer, and it's very hot. Most of us are working outside in the hot sun and sweating. Meanwhile she gets to stay inside and do things like bagging while in the air conditioned store. I've talked to coordinator about this, but even when they talk to her they barely get her to do anything. Is there someone I can contact about this?