One thing Walmart does well is promote from within. If she was a good employee she would have been promoted before now.
Based on her pic, she’s probably not physically able enough to do the more active jobs around the store, such as stocking any of the departments (especially grocery or garden), or working in one of the higher-volume areas like electronics. That leaves greeter or cashier, or things like that. She may be limited as to available areas. That of course doesn’t exclude your premise; even within her viable areas she obviously hasn’t excelled, though it might be harder to stand out.