Okay, the only way this works is if the slave crest changes your attitude. Otherwise there is absolutely no reason why she should decide that she would become his slave. She doesn't even know him except for like 30 seconds worth of time when she was dying. That's far too short of a time for you to decide to dedicate your life to someone. Using the "your only other choice is execution" excuse doesn't really work when the person in question already doesn't trust humans. Especially when Ana referred to her as a "thing" while she was pinned against the wall. What the hell is going to happen when she runs into Princess Ana again?
What is Kane going to do once he finds out that his new servant had a sword through her belly and that's the reason why he had to save her. What's also strange is although it's "normal" that Ana doesn't think things through to that extent, it's uncharacteristic that Maya didn't think about that detail. She already questioned Maya about Dustard. Is she going to do it again now that there's no more slave crest? If so how do you run that by Kane? Just say "hey we were the ones who put her in that state and we need more information". There doesn't seem like there would be a clean way to handle that situation.