Your reasons for holding off discussing a grade skip with DD make sense. As for the letter, I thought the wording was good. The only part I'd change is the last sentence. Something about "the need to bombard you next fall" might not be well received. Maybe this?

I know that the beginning of each year is extra busy for teachers, so I'd like to work together now when there aren't as many time pressures. I appreciate your help and look forward to your response.