SenecaFalls - that article was the first that showed up on a quick'n'dirty google. But I do recall other articles at the time when the Queen issued updates about who was to curtsy to others. And it was quite complicated because it all depended on whether the husband (for married-in women) were there or not.
I recall one article with a photograph of the Queen arriving somewhere and William and Kate did the knee-bending but Beatrice and Eugenie didn't. The article explained that B&E had already curtsied to the Queen that day, so didn't need to do that again. Presumably that curtsying by B&E happened in private. Yes, that curtsying was to the Queen. But why would it be necessary to stipulate when Kate curtsies to Camilla, and when Camilla curtsies to Kate? I don't think the absence of photographic evidence helps, because all that bowing and curtsying would be in private. And the Queen is a stickler for carrying on the protocols established by her mother.
PS: I love your screenname. It's only in recent years, from getting into history, that I recognise the significance.
QueenOfTheAndals - That was cringing. Teresa May should know that it's a constitutional monarchy. Just a brief bow would have sufficed. It's demeaning to women to have to abase themselves that way, let alone a female Prime Minister.