I don't have much to add, except that our school district required an impartial school district representative from a different school to attend all IEP meetings... no doubt due to the school district having past history of not following the principals of IDEA... perhaps...
Anyway, in your case - if you hear back from the principal that the gifted teacher can't attend, remember that you can still make a list of the strategies she's found to be successful when working with your son and *you* can bring them up at your meeting and request that they be added to his IEP. If the school tries to counter, you can always say "We're stopping this meeting right now, and will continue it when we can reconvene with ____ present".
Good luck with your meeting!
polarbear
