First of all, just a doubt:
It's said that "Margot" was a name wich took his origin in the XIX century, invented by Dumas. But:
1) It's said too that Marguerite and all her brothers and sisters had nicknames when children, as Sandrine, Margot etc. What are the sources of these stories?
2) The story of "the king Margot", the young lover of Marguerite once in Paris after her return from Usson. If it's true, there must have been a queen Margot behind this story.
3) In a XVI book describing the forteresses it's said that Usson in Auvergne had four towers, and every one is called by her name: one of them "Tour Margot". It's a contemporary document, because few later Usson castle was rased. So?