Hahahaha, i think that some Mary stans are so nuts than even argue about the health of Edith´s daughter; the thing is that girl is a toddler 2 years or somethink like that and you expect that she should act in the same level than Maggie Smith? Put in the place of those kids, people with rare customs, the cameras (cranes and all that sort of equipment), their mothers in the other side of the camera. Even more, there is a pic of the boy who portrays George with Michelle Dockery and Kate Middleton and he seems to give a fuck about that he is possing with is the duchess of cambdridge and he has more attention to a toy; so using the logic of some people here we can say that he is a republican who disagrees with the notion of royal family?. In the end of the series we can see Marigold running a playing with the others as any normal kid of her age.
Back in the series, of course that her origins are a serious business, the thing that Edith and Bertie must be worried is that the circunstances of her birth dont ever be public. In England as many other countries, childs born out wedlock were common, for that reason all type of families invented those histories, like being a ward, being a child of a distante relative, the thing is many people (like the servants or others) could suspect or know, but very different is the confirmation and public knowlodge. About that Marigold couldnt be presented in court, again some people forget history, Marigold would have 18 in 1939-1940, in the middle of the second world war, in those times all presentatios were suspended in the same way that the first world war, the king and queen of england didnt have time to debutantes because they had to go to cheer the people bombed in London; also the society in general was not in mood for debutatnes balls and those things.