@ Val — I hesitate to question the optimality of your daughter's choice of activities without solicitation & hope you'll forgive me if it's unwelcome, but have you and her thought about whether spelling bee preparation is the best use of her time?

Training for spelling bees may build discipline, constitutes cognitive exercise, and if done in the way that she's doing it, can improve one's understanding of language. But there are more conceptual activities that utilize higher order thinking skills to a greater extent. And very few people gifted people (or people more generally) pursue professions that utilize the subject matter learned to a nontrivial degree.

I tend to think that it's better to learn

(a) Ideas that have broad ramifications (such as some of those from psychology, philosophy, economics and evolutionary biology), or that fit into rich conceptual structures (such as those from math or physics)

and

(b) Skills that are useful in many real life contexts, such as writing, and programming.

There may be important considerations in favor of spelling bees that I'm missing, and I'd be interested in hearing any. I recognize that gifted children are often involved in spelling bees, and that there may be social benefits to being involved even if the activity isn't the most valuable in the abstract.

children who are 10+ years ahead in math

I don't know children who are anywhere near 10+ years ahead in a social science (nor adults who were as children) ... don't have a good intuitive sense for what's going on from the inside. What experience do people gain as they get older that prepares them for social sciences?

What experience do people gain as they get older that prepares them for social sciences?

The 1996 study Self-Efficacy Beliefs and Mathematical Problem-Solving of Gifted Students found that

Although most students were overconfident about their capabilities, gifted students had more accurate self-perceptions and gifted girls were biased toward underconfidence.

Facebook chief operating officer Sheryl Sandberg discusses high potential women being underconfident in her book Lean In.

I've had many gifted female students and classmates/colleagues who have struggled with intellectual insecurity.

Not gonna stop me from buying DD STEM toys or encouraging her to flower in that direction but...

Reality of differences between boys and girls

And, as Geary recently told me, “One of the largest and most persistent differences between the sexes is children’s play preferences.” The female preference for nurturing play and the male propensity for rough-and-tumble hold cross-culturally and even cross-species.