It sounds like the teacher is doing a lot of work to make things better for your DD. Just a warning to try to make your communication very thankful to this teacher, with attempts not to take away from what she's doing. We made the mistake of having a meeting with our DS's previous school team where we told them that he needed more, and the classroom teacher told us he was very offended, because he'd been working his butt off to differentiate for our DS (and this was after the grade skip). It is always difficult to walk this line. For us, it was more a miscommunication issue, but what it came do for us was an understanding that what our DS really needed was 1) faster pace and 2) intellectual peers.
Perhaps you can say something like, "We are so grateful for everything Mrs. T is doing. Our DD is much happier to have some work that is closer to her level. We feel that things will be even better next year if we have a grade skip into x grade, where more of the base level materials will be closer to her level and there won't have to be as much differentiation work for the teacher. Also, there will be a greater chance of having other kids working at DD's level."
Lots to think about! I do think you are very lucky to have a teacher willing to do so much for your DD now. In contrast to Grinity, I'm a fan of email versus paper letter - you can cc emails to many people. We've never had to write a formal letter, and if things are going well with the school, I would say start with an email. Formal letter if you get no response. Emails can also be forwarded along quite easily, when necessary...
