Sue is trying on her new wardrobe for Grey and her secretary. Grey notices that she's still wearing her cruddy shoes. Sue holds up the fancy shoes and asks "you mean these." She then begins to crawl on the floor and scratch herself. They cut to Grey. They then cut back to Sue, who's now wearing the fancy shoes.
When Grey comes home from work and Bill is still gone she corrects Sue about her language. Sue is wearing brand new Nike shoes, yet she is clearly dressed in Grey's clothes not new ones of her own. The shoes mysteriously appear before the shopping trip. Then when she gets taken by social services she is in her cruddy old shoes again.
It is revealed that Susan can't read, yet when she and Bill take Grey out to eat they check a banquet listing directory and it is Susan's finger that scans the listed parties and chooses the one they attend. This seems to indicate that she can read.