But I think the most important consideration here is actually (and I am trying to say this as gently as possible) the distance between you and your spouse regarding this parenting decision. For most children, almost any non-abusive schooling situation will be at least bearable, as long as her parents are united in supporting her through it. If she senses the discord between you regarding her education, the risk is high that she will begin to believe that she is the cause of conflict between her parents, which, I need not say, will be far more damaging than anything an educational mismatch may do.
Please believe that I am not judging you--we've all found ourselves in situations where we've cared so much, or been under such stress, or been so exhausted, that we've lost perspective. I do encourage you to take a step back, find some time to have a private, uninterrupted mutual listening session with your spouse, and get on the same page. It is apparent that you both care deeply about your child. Start from this point of agreement, and you will, given enough time and listening, be able to find common ground.
This.
IIRC you and your DH have a history of coming on this board to complain about one another? And you have been stressing out about middle school and accelerated placement for years?
This grade skip sounds successful! She is getting As. She is happy. She has friends that SHE feels are friends. Take it year by year.
And as far as having no access to the actual reading teacher is concerned, this does not sound like such a hard problem to solve. This can't be classified information. Phone the school.
Also, as far as I understand (I do not live in the US) it IS only math where falling off the accelerated track could create problems down the road. There is no such clear cut progression in reading or English lit, right? Or does your school system actually do that? The one I live in actually does, and not making accelerated track for middle school could be a disaster for some kids, but I'd be very surprised if things were set in stone by fifth grade in yours, as you appear to be worrying. A school this large must have tons of options and flexibility.