I don't think that it is ever too late to talk to the teacher especially since it's not just you wanting her to be challenged. She seems truly unhappy and that is important. Whether the teacher does anything about it, at any time really, is completely up in the air. I do appreciate your concern about the timing because there are many teachers I have talked to that say if it is after the 1/2 way point they will push you off until next year. I still think it's worth trying. Can you explain to your DD what you think the problem is? If she was working with you it might have a bit more impact.
Good luck!
