I can't forgive Lanz for abandoning her nine year-old sister. Especially when Lanz doesn't have anything remotely resembling an excuse for taking off. There was no crisis, she wasn't faced with a difficult decision, she just left because she thought she'd like it better somewhere else. We learn this quite early in the story and for me it made Lanz such an unlikable character that I didn't care what happened to her. I would have preferred to see the events from someone else's point of view.
Of course the story shows some family history of abandonment. Lanz and Ria's mother abandoned them when they were fourteen and six. It's possible that this is just an extremely dysfunctional family. But given the world of the story I can't help wondering if the presence of the all-knowing, all-powerful AI was part of the reason for the abandonments. Were the mother and Lanz unconsciously relying upon Kaysee to protect and take care of the children they abandoned? I think they must have been. Otherwise they were horrible, terrible people, not people a normal person could understand or be interested in.