I think your recent update that it is a group of kids vs just your child sounds like a better fit!
We went through some similar stuff with DS10(almost 11). Mainly our pressure came from family. His private school has very strict restrictions on cutoffs. Socially he would never had been able to cut it if being moved up was an option. He does get teased about being "so smart" but the kids also make sure to pick him first when group project time came around.
His teachers have been wonderful, they have allowed him to assist the other kids in class who are struggling. He really enjoys this and this has given him a new sense of confidence and helped with his much needed social skills. Also there is a great deal of craziness from parents when there child does not get picked for advance classes here too.
DH and I decided not to "challenge" anymore with school work, DS does enough on his own. We didnt want him getting too far ahead of his peers. Advanced reading at his school didnt start until 3rd, and Honors Math starts 5th grade for him this year.
We challenged him physically, DS LOVES sports, but this is not his strong area, he can succeed with hard work (unlike academics where it is super easy), so he can understand that although some things come easy to him some things take hard work. We are hoping this lesson can be applied if and when school becomes the challenge. We rotate the activities as well.
Maybe reducing her dance a tad (not too much since she does love it) and put her into some other activity (doesnt have to be sports) that could challenge her may be somehting to consider.
Dont beat yourself in the parenting area either. I have no idea if what I typed above is the right thing for my kid or not but it feels right. We are all flying by the seat of our pants.
Also I did read your trip report awhile back, I would be cautious with Cat. Even though she was a perfectionist before, she did have a tough time when you and your DH separated. She may be using the things in her world as an attempt to control what she can, bc there are many things at this point that are beyond her control.