Personally, without an extremely compelling reason, I'd be pretty reluctant to take a gap year just for the purpose of trying to reapply to a school like MIT.
Sorry-- but I just don't think that your odds are going to be appreciably better in a year. The college admissions arms race gets worse annually, from what I can tell.
Plenty of the students applying at those schools that reject 95%+ of applicants have paid assistance in preparing killer applications from top to bottom. That's reality now. If you're truly determined-- hire a writing coach that specializes in this kind of essay and have him/her spend a few hours with your child and her essay.
The edge that a young graduate has in terms of lifetime earnings is significant, let me add-- and a gap year definitely takes away one year of the gift of time that grade acceleration has given them-- so be sure that they WANT to spent it in that way and at that time.
