That's the thing with Fey, or all creatures for that matter (not sure if it applies to eldritch tho).
After scraping through discussions in the discord server I've gathered this info.
All creatures have a "true name" and a "public name".
Fey know their true name since birth while humans are completely unaware of it, without any real way of learning it.
The public name is given to them by their parents (or anything resembling a parent) but also they may pick it themselves at some point in their lives.
We don't know the true name of anyone, no fey has ever given us their true name and most likely no fey ever will.
Because knowing a fey's true name is a way bigger deal than it sounds like.
It would basically mean having absolute control over someone, to an atomic level, you could even wish them out of existence with that amount of control over their entire being.
Kind of like having admin access to their existence.
Which is why, no matter how strong your mind control powers may become, you can't force someone to give their true names.
You'd need absolute control over them, which, you know, you'd only have by knowing their true name already.
That's why I don't think we'll learn the true name of anyone during the course of the game, that'd be giving too much power to the player without any real way to use it.
As for Pixie... It becomes evident she picked the name on the spot.
I mean, putting aside the fact that I'm not sure she's even a pixie.
Morgana considers her a failure, so why would she ever name her.
The other staff members don't call her Pixie either.
IF we ever learn her name, it might be in the epilogue of the game.