Not to mention that strange animal behind her. It can't possibly be intended as an orang-utan. I guess it might be intended as a Thing from the Dungeon Dimensions. Still, it does give the general flavor of the story: child with powers and a staff, witch mentor, weird critters. I've seen worse covers.
Back to WA: Although Granny thinks she's being kind, and Lily seems to take it that way, I'm not so sure. What if Lily had accepted Granny's offer? She'd be back in Lancre, where everybody knows she was kicked out, not just for being wanton but for severely breaking the rules of witchcraft, misusing her magic to compel people's obedience. She'd be beholden to Granny for a place to live, and everyone would know it. And she would have lost, and would have had to live there knowing she'd lost and that everyone else knew she'd lost - a classic witch revenge. Frankly, the mirror universe is a kinder fate. At least there she theoretically has a chance to figure out who she is and escape. She would never escape Lancre again.