I sort of hesitantly agree with what you are saying. In my, personal, opinion, she should have been involved with the adult class in order to learn the things that she should know about off-balancing a larger, stronger opponent. I would have started her in the adult class as soon as she was, say, an ikkyu level in the children's only class, if your school has such a thing. Then, you would be teaching her not only the adjustments she'd need, but teaching her at a, generally, more advanced, more mature level all around. That is JUST a personal opinion, so don't tell your Sensei that he did wrong.....