If the test revealed she had a Y chromosome, whether she is XXY or XY (and that has not been made clear at all), she may not have even known. And any partners she had would have thought she was cis as well.
Brittney Griner is as "manly" as Imane Khelif, but only the craziest of the TERFs claim she's not a woman.
The question that I don't think society has wrestled with, and I'm including both left and right wing people, is who should be allowed to do women's sports? What's the purpose of the competition?
Imagine a world without male and female events. Instead, every category is open to any athlete who wants to compete. In that world, very few Olympic events would feature any female athletes at all. You'd see some in equestrian events, some in shooting events. In most other sports, having a male body is enough of an advantage that you won't see many women at all.
So, the purpose of having a women's category seems mostly to be allowing women to have a chance at winning something by not having them compete with men. That means you have to draw the line somewhere. And, wherever you draw the line, some people are going to be left out.
Who gets to decide where the line is drawn? Different cultures have different ideas, and at something like the Olympics, every country is represented. Historically, it has been men deciding who's female enough to be allowed to compete. I think most people could agree that that's bad, and it should be women making that decision. But, should it be all women, or only athletes who are actually competing in a sport? If it's left up to the athletes, isn't there a chance they'll want to draw the line somewhere that favors themselves?
It's always going to be a sticky situation because the whole point of a women's category is to keep out another group who would otherwise have an advantage. But, there's no obvious line that can be drawn that everybody will agree with that separates the two groups.
While this reads and sounds reasonable, in reality it is anything but. Because what it boils down to is that women are not allowed to be successful on the same terms as men.
If a male athlete stands out over his peers through unusual body features and physical advantages, that's fine. But if a woman does, then you immediately get people questioning if she's really a woman.
The gender policing of successful female athletes is not new - it has a long and dreadful history. Athletes like Martina Navratilova, Venus and Serena Williams, even Simone Biles were subjected to this at some point in their careers. For some women it has led to significant disadvantages and loss of opportunities purely based on conjecture.
Also, this kind of policing is often done by women under the pretence of wanting to protect women - but hurting women in the process. Some women don't care that they're hurting other women. The key problem is that womanhood gets redefined all the time and narrowed at will depending on who currently rouses someone's ire.
So for what you're proposing to work, the criteria must be simple, wide-reaching, and unassailable. They must not discriminate against women with unusual physiques or body features so long as they are clearly women. Gender determination cannot be intrusive or demeaning. Anything else hurts all women and entrenches their systemic disadvantages.
It'd be cool if instead of grouping people and doing direct comparisons, we scored them on how well they did relative to their physiological features. Kind of like how Wilk scores were used in powerlifting. I don't know how feasible it is, but maybe something based on testosterone levels could be done.
I think there are plenty of people who understand how to place trans folk into gendered sports is a complex discussion that needs to happen - You'll just NEVER hear them over the "NO MEN IN WOMEN'S SPORTS BUT ALSO NO WOMEN WHO ARE TOO GOOD AT SPORTS BECAUSE THEYRE MEN TOO IVE JUST DECIDED ALSO ALSO NO UGGOS" crowd.
A lot of "male" events are actually open for anyone, it's just that women generally prefer women only events, since women will usually be at a disadvantage on average.
It's wild. I had a high school biology teacher in 05 do a whole class on intersex stuff, including what you mentioned and mosacism. It really drove home how complicated sex is, let alone something more abstract like gender. No way she'd be able to teach that now.