Is this Doctor Who character the Nightmare Child?

Question

In series 9 episode 6 of Doctor Who, when the Doctor revisits

Ashildr

she’s known across the land as the Nightmare.

I watched a YouTube video which goes through Doctor Who easter eggs, and it says that she is the Nightmare Child, as in the one Davros flew his command ship into the jaws of.

Now surely that is totally wrong. She’s human, the Time War is over, and she can’t grow to a size a command ship would fly through. Doesn’t it have to be the writers using a play on words? Or is

Ashildr

really the Nightmare Child?

Answer 1

Highly unlikely.

The Nightmare Child is a vague, unspecified threat that the Tenth Doctor mentions, along with a laundry list of other horrors, that the Daleks or Time Lords unleashed during the Time War. We have no idea what kind of creature this was, or if it was even alive. But what we do know about it is:

• It was "born" during the Time War. Ashildir most definitely was not.
• At one point, was was going to be called "The Dalek Emporer's Nightmare Child"; though that never made it on-screen, it reinforces the general principle that the Daleks Created this thing to fight the war. Again, Ashildir began her life as a normal human child.
• It was gigantic enough to swallow a Dalek craft. Barring some ridiculous physical transformation, that's not Ashildir. It's not out of the question for something like that to happen, but it certainly had not by the time she earned her nickname.
• The Nightmare Child is locked away in the time-locked Time War. This was the entire purpose for The Doctor's actions in "The End of Time". The return of horrors like the Nightmare Child would have meant the end of the universe; Ashildir's presence hasn't done that

Nightmare is a very generic, commonly used term in fiction to describe something terrifying. There's almost certainly no relationship between the two things.