Songbird,
Its going to be very hard to accomodate her when she is in the slow lane 8+ hours a day.
I was radically accelerated and enjoyed it. I can understand the fears of being exposed to too much, but my parents told me to just get up and walk away if I started to feel uncomfortable.
My DW was skipped a grade ( 1st) and feels she could have skipped again from 7th to 9th grade. She feels now that because she was not challenged, she just gave up on school.
It does not have to be cold turkey.
You can do pullouts to other grades, ie from 2nd to 4th for reading and math and see how it goes. If she knocks the ball out of the park and make friends there, then consider starting her in 5th grade this fall.
