Sure, I'll bite.
Is this an in-universe reason, like something Eva would say to dispel rumors? In that case, she could say that she got close to the family decided to adopt him and let the family live in the main house. It sounds like something she'd do.
If not, I don't really know. Well, giving him a normal life is a good reason. I'd stick to that. (Mostly because I can't think of anything else but oh well)