First, welcome. I am very sorry you are having to go through this. But many of us here have been in similar situations and feel your pain and frustration.
Do you have copies of the testing they did when considering early enrollment? If not, request those immediately from the school psychologist. You mentioned that the school psych said your DD was definitely mature enough to enter K, so maybe some of these thoughts are included in the testing summary. They would be important to be able to point to when the teacher is saying she is immature.
Dealing with a teacher who is so unsupportive of your DD being there is going to be very difficult, if not impossible. I wonder if the principal knew this, and that is why s/he chose not to tell the teacher your DD's age. I could see how they thought this might be a good idea (my DD, for example, prefers to blend in and doesn't like to have her age become known until people have already gotten to know her and her abilities), but it also shows a lack of leadership by the principal. Still, perhaps the principal is still on your side, but having trouble with the situation because s/he is only getting the teacher's side of the story. If you have already tried to talk to the teacher to work things out - and it seems like you have - I think you should request a meeting with just the principal and you and your DH. (BTW: If at all possible, both you and your DH should attend to present a united front.)
Is the meeting next week a regularly scheduled meeting to check in on how things are going, or was the meeting called in response to the teacher's problems?
BTW: It doesn't sound like your daughter is really all that asynchronous to me. I just think the teacher is looking for anything she can to justify her preconceptions about young K students, and your DD specifically. The teacher thinks your DD doesn't belong there because she is so young and she is darn well going to prove it whether it is true or not.
Personally, I think the teacher sounds toxic and that your DD should no longer be in her classroom. I would ablsolutely request a different teacher, and request that you and the principal meet together with the new teacher ahead of time to discuss your DD and her needs and make sure the new teacher is on board. That could make all the difference.
