Rodan is, of course, the name of the young Gallifreyan who The Doctor meets in the TV episode, Invasion of Time, and whose scientific knowhow helps save the day.

Rodan Mielles, the baby Marion and Kristoph take on as a foster child is not that Rodan. She would obviously be older than The Doctor, and not a young Gallifreyan female when he is on his fourth regeneration. This is her mother, just as the Romana of Chrístõ’s acquaintance in Theta Sigma is mother of the Romana he meets in the same fourth Regeneration.

One or two people have pointed out that Mielles shouldn’t be her surname, since her mother is Argis’s daughter and she must have been married to somebody else. Yes, that’s a plothole. Let’s assume that, having gone to live with her grandfather she then takes his surname for the sake of things and not worry too much about that.

Why does Gallifrey have a freight service that takes months in deep space when TARDISes can travel anywhere almost instantly? Because TARDIS travel is for the rich and privileged of Gallifrey and ordinary trade with other planets is done the way it has been done since Marco Polo. Kristoph is rich and privileged, of course. Catching up with the freighter in order to break the bad news to Argis is easy enough for him.

Kristoph’s relationship with the people of the Lœngbærrow demesne as demonstrated here, of course, is that of kind, generous baron of a feudal fiefdom in the Middle Ages or something like a nicer version of the landowner system of Ireland and Scotland pre-famine/clearances. He considers the people who live on his land, work the mines, serve in his house, as part of his extended family, and certainly his responsibility. Hence, he takes on the welfare of Rodan after her mother is killed.

Exactly what sort of accident befell her mother, I decided not to get into. It really doesn’t matter. The point is that Marion, not long after losing her own child, had a baby to look after for nearly two years. Yes, there is going to be some heartache later. But for now, she is happy and Mothercare Liverpool’s profits have gone up exponentially.