The big one I would suggest is some sort of pretest to start he in the curriculum with where she is, so she can skip the "easy" stuff she already knows.
That was our big problem with the Montessori school we had DS6 at. It was just too lockstep, and they required proof that he could complete step A, B and C, even though he was already at step Q! He did nothing in the language arts area for half the year because he was reading books and they were requiring that he learn letters, something he'd mastered literally half his life ago!
So pretesting to skip easy stuff would be my suggestion.
