I commiserate with your daughter as an adult. I didn't bother dating until university, when a 3+ year age difference with class colleagues helped me meet my now-husband. Over the years, I've had many friendly acquaintances (other people's "good friends") because, like your husband, I'm athletically inclined and extroverted. I'd count 3 friends among those, including my husband, who truly "get" me and vice-versa.
I don't think that that pattern of socialization, or the paradigm of life-mates that you describe, is atypical for HG+ individuals. Assortative soulmating-- platonic and otherwise-- appears to be our dominant strategy. Frankly, it's just a reality that stems from being part of a statistically rare group. My take is that our role, as parents, is to instill self-confidence and self-esteem in our children so that they can independently weather the inevitable loneliness that comes with being...different. Your daughter sounds wonderfully well-adjusted, so this is probably redundant.
On advice for words to share with a 13-year-old, the following comes to mind, though it may or may not jive with your thinking:
The headmistress at my all-girls high school made a provocative statement in the fervour before prom that has stuck with me over the years: "Men are like handbags; they can bring you enjoyment, but they aren't necessary." (I think the statement could equally be reversed wih a gender-appropriate analogy for an all-boys audience.)
On opportunities to meet peers, beyond the great ideas listed, many universities offer intensive spring break/summer sessions for high school students. Maybe you could advocate for early placement in an extracurricular forum like those?
