I wouldn't really worry about a 'big drop' - if there are sensory issues that are being treated, then there may even be an increase (hint, hint - do the OT first, then get the new IQ)
It is harder to 'blow the roof' off the test, but not harder to get into the 95% in general. If you want to be cautious, pay for the IQ test privately, and you don't have to show the school if it was an 'off day.'
Congratulations to you for moving her to a Math class where she has to actually work.
I would suggest that if she isn't typing yet, to hothouse the touchtyping. That is a huge timesaver for my pokey-slow DS14.
I would also suggest that if she hasn't yet done the SAT through the talent search, that now is the time. She might enjoy CTY camp, and it's great to see how they grow. Of course time will be an issue, but hopefully once she is retested, she can get additional time on her 'real' SATs.
Best Wishes,
Grinity