And it took me a moment to figure out why your objections didn't bother me, although they would almost certainly have irritated me in professional fiction. First of all, this was a story whose premise was very ship claustrophobic. It's got an extraordinarily tight POV, and the only other major character is Rodney. This was not, in any real sense, a story about Hypatia, it was the story that Hypatia catalyzed. So, I wasn't at all upset with the development. I never felt as if shallot had promised me a story about an adorable precocious child, so when she was used as a secondary character, I didn't feel cheated.

Secondly, her characterization was handled as if she were a canonical character. We were told what we needed to know about her and her reactions to make the story we were reading work, and the rest was left unsaid, as if there were greater canon information about her available. That sort of sketchy characterization, where we are focused mostly on how a character acts in particular kinds of situations instead of in the general case, is a very fanfiction way of character presentation. I'm surprised to find that it worked for me even in the case of this original character, but it very much did.