I hear you. I remember arguing for more for my kiddo before we found our right fit school. I remember specifically asking for a chance for him to fail, so he can learn to persevere. I can see how you're in a tricksy spot, since the school "knows" gifted. Is there one particular area you could focus on for a "test" area, to see if your DD could be moved up a grade for that class to see if it's more challenging? Maybe start by saying something like "thank you so much for all you've done for my DD, she is the happiest she's ever been in school, but I still have this nagging worry that she's not going to learn what to do if she fails, as she seems to still get everything so easily. Any chance we can move her up a bit?"
I think sports and music lessons can be pretty good. For us, our DS learned some of that feeling of success after working hard through piano lessons. Maybe an outside of school academic class, even online, could help if the daily school isn't enough?
Sorry, no particular advice on the girl front, as I have just a DS. Also, I was an underachiever myself, not being challenged until college. So I can completely relate to all the efforts you're putting in to find a good fit for your kiddo!
