Where Every Scroll is a New Adventure
It annoys me when people say that Jest died because Cath decided to save a traitor. Mary Ann was her best friend. She was one of the few people who she loved and who loved her back. Mary Ann was confused and didn't know what to do. The nuance and heartbreak that is Cath's decision to go through the door and save Mary Ann is what's so compelling about Heartless.
Yes, the prophecy was going to be fulfilled, but what was she supposed to do? Let Mary Ann die? The deepness of her decision comes from the fact that whatever she did, someone she loved was doomed to die. That's why this is a tragic story. Whatever Cath decided to do, someone was going to die. And yes, Mary Ann was impulsive and scared, and you could interpret that she "betrayed" Cath. But when was love conditioned by loyalty? Cath loved her, and she couldn't just leave her there to die.