It did annoy that she went to Givenchy.
I was disappointed by that on the day - and I liked and supported them at that point. For such a high profile occasion it should have been a British, or Commonwealth, name.
I don't think the tights thing needed to have anyhing to do with protocol. I can think of several reasons why as a parent Catherine might have wanted Charlotte in tights:
May in England can be chilly. If it had been a cold day, bare legs would have been miserable
At Catherine's own wedding, when the bridesmaids were sitting on low stools, while the service was in progess, one of the small bridesmaids fidgeted so much that if she hadn't been in tights, her knickers would have been on show, to a global audience of millions.
Charlotte had only just turned three. Even if she was normally reliable, Catherine might have wanted to put her in a pullup for the occasion, just to be on the safe side. Tights would have concealed it.