I'm not OP and I have no idea what the actual odds are. But, well, only 15% of Americans are black to start with, and obviously only half of those are women - and at that point we're already down to 1 in 14. So, unless every other black woman is a queer mom, there's no way it's 1 in 28.
If you were trying to mimic a distribution of Instagram users, and you rolled the dice 28 times, it's not unreasonable that this combination of traits could be expected one twenty eighth of the time.
