Since she can go to the STEM school the following year, and that school would be a good fit, I don't think I would go for the skip. The adults I know who were grade skipped (especially those who had multiple skips) all seem to regret that they "missed out" on something. For some it involved the social aspects of school, for other it was sports, etc. The stuff like sports, academic competitions, music competitions, and prom only come along once. You do them while you are in school or they don't happen (except perhaps for a select few).
Yes, if you get injured you can still become a scientist. However, you can still be a scientist if you don't grade skip. But you can never go back and try out for the basketball team or all-state orchestra. You don't get a second chance at PSAT/NMSQT.
My concern would be that years later as an adult, my kid would say, "If you hadn't grade-skipped me, I could have ." I don't think a nine year old kid can see the potential consequences. Heck, my 17 year old can't see why we recommend she do certain things to improve her chances at getting into the college of her choice. And my 19 year old now says she wishes she had done certain things in HS...the very things we recommended she do.
