Well, Rich just wrote back and let me know that she is, indeed, around 9 months old and is a stellar eater but a slow grower. He also said that she is probably from a clutch that all hatched out small.

So I'll give her the week to settle in (which may take the whole time since she's still testing every surface of her tub), then start her on a nice schedule of every 5 day feedings and see where she goes from there.
Guess I won't be doing any breeding for a few years...