How did he manage to get her to stay behind to begin with? Did his house have that much authority?
Your question ties well together to what I was going to comment on anyway and what Adel noted himself: Kate is quite childish. I was wondering how she could let a visitor inside her room while wearing only a camisole, but it was probably also due to that same fact: she's not really a mature woman inside, even if she's one outside. So, yeah, it shouldn't have been too difficult for Adel to make her stay behind when a part of her mind is that of a child. Not even a mean-spirited child, but rather a kind and friendly child.