Since they will be testing her before placement, I don't think you need to worry about gaps. Besides, there is so much spiraling in the elementary curriculum that she should be able to pick up from 6th grade math without too much effort even if there are a few gaps. 6th grade is technically middle school in our area but math-wise I would still group it with elementary math. In most curriculums, 7th grade math is pre-algebra although I have seen some "delayed" curiculums with 8th grade math as pre-algebra. In our district, normal GT math uses the textbook that is one grade level ahead along with enrichment but a number of kids are tested out of 5th grade GT math (6th grade math text) into Pre-Algebra as 5th graders. Since my DS was already accelerated in 2nd grade, he tested into that pre-algebra program as a 4th grader. Anyway, my point is that the consensus seem to be that it is okay to skip any year of elementary math (K to 6th) but not pre-algebra.
Since you have been reassured that 2E will be fully accomodated, you really don't have to worry for now. I would let middle and high school take care of themselves as there may be other options once your DD reach that level.
