"Is she a child" is exactly how I see her and at the same moment, Liam appears more and more as a creep and a groomer. The interaction with Jake just makes me wish she'd go with him instead of Liam, at very least I believe it would have given Sora plenty opportunity to mature during her travels. As it stands, I am actually afraid for what might happen during her travel with the giant.
With the sex drive that Oni's are depicted to have early on he must be dumping quarts into the toilet to resist when sleeping with her as the Big Spoon.