I think if it's the tradition for little girls at Royal Fam events to wear tights then Meghan should have allowed the flower girls to wear tights. When in Rome, do as the romans. This becoming a sticking point makes it look as if Meghan was unwilling to learn about royal protocol.
This would tend to fit with the description that Meghan gives that she went in for a hug first thing when meeting Kate/William, and hence offended them. There's nothing wrong with being a hugger but I think hugging someone you just met is overkill. It's a bit dominating even if you do it to just a regular person, as it shows an unwillingness to listen to whether the person you are hugging will be uncomfortable. Would it have been all that impossible for Meghan to see things from William's POV and realize that, until he knows her well, she's one more person who might leak very personal things about him? Of course William would be reserved around Meghan until he knows her better!
That said, from the POV of William and Kate, they're meeting Harry's beau for the first time, I would think good manners would dictate they make Meghan feel welcome to the country and to the family and it kinda seems like they didn't. They must have known the UK Royal Family would be a dreadful culture shock to her and that she would feel very isolated in that environment. Even with the most generous interpretation I can make of their choices, they come off as rather cold fish.
And coming to the crux of the problem, if these people really do curtesy to their "superior" family members in private, no wonder Meghan got out of there as fast as possible. Meghan is an American. We're all equal here. She could be president of the USA if she got elected. To go from that, to curtseying to other men and women just because of accidents of birth, that would really stick in one's craw.
The problem with the fit of the flower girls dresses was created by the person responsible for overseeing the making, fitting, and alterations of those dresses. I don't know if we'll ever know who that person was. Was it a palace staff member, someone at Givenchy, Meghan herself? Oh, who cares, let's move on.