On the one hand, you hear Russian and Chinese coaches say that girls have to master as much technical difficulty as possible before hitting puberty, so that during/after puberty, they can just work on maintain their technical difficulty (since improving on it after puberty seems really hard). On the other hand, what makes learning new elements hard at a later age is not only because of the more womanly figure, but also because of aging. Sad but true -- but in late teens the brain is already not as plastic as pre-teens or early teens, plus a certain self-consciousness and fear set in, so that learning a complex, dangerous motor skill becomes that much harder. Maybe someone like Nina has the best possible scenario: go through puberty really early so that she will not have undergo much bodily change during her teenage years, AND still be young enough to have the neural plasticity and youthful fearlessness to master new technical skills. I really hope so anyway! Because to be competitive on the international scene, she will definitely need to up her technical difficulty significantly.
I actually cannot really think of many female skaters who had so much of their growth done by 13 -- I mean, it's possible that she will grow 5 more inches and fill out a lot more, but it seems unlikely.
And I agree with you that 2A-3T could certainly be part of her game plan. Her 2A is so secure. If she can do 3T-3T in the SP, then she can certainly go for 2A-3T in the LP. The 3T-3T looked pretty effortless ; 2A-3T has got to be even easier for her.