How often does that happen? 1 out of 10 million births?
No, actually between 1 in 40,000 and 1 in 120,000 children born presenting as female have an XY chromosome pair and complete androgen insensitivity syndrome.
The point is, no one cares about what chromosome pair the person in the next shower-stall is carrying when they go to the gym, they care about what genitalia they exhibit. The XY-CAIS girls have been showering with normal XX girls from time out of mind and no one was unhappy with the situation.