Ultima behind everything?

[Iscah]

I’m going to go out and say that it’s probably not that deep and that Cylva never actually turned into a wolf monster just like Thancred never turned into a snake angel thing (taken from Ryne’s memory).

Those aren't equivalent things though. The Shadowkeeper wolf is supposedly Mitron's recollection of the fight between Ardbert and Cylva – a real historical event. The Fatebreaker, on the other hand, is explicitly an amalgamation of things from Ryne's memories – not just Thancred but also Ran'jit and apparently the sin eaters as well.

And there is precedent in the game for people actually transforming into wolves, and a connection between wolves, wargs and the Shadowkeeper.

FATE "A Beast Among Men", where you fight a Fenrir-type wolf:

Once upon a time, Lugarhoo traded obedience to the Shadowkeeper for the power to rend his foes with tooth and claw. Now freed from that pact, it may appear that little remains of the elf he once was─but, in truth, the thirst for violence was always at the heart of him.

FATE "Cry Not Wolf":

Though the wargs born to serve the Shadowkeeper's fell purpose have long since cast off the chains of that fate, they resent what remains of mankind quite as much as did their erstwhile master, and are eyeing the Forest of the Lost Shepherd as a venue to vent their ire.

It's possible that showing the Shadowkeeper herself as a wolf is creative licence, but also quite possible to be a form she actually took.

[MikkoAkure]

Those aren't equivalent things though. The Shadowkeeper wolf is supposedly Mitron's recollection of the fight between Ardbert and Cylva – a real historical event.

We see both the beginning and the end of the fight between Ardbert and Cylva and both times she's wearing armor and wielding a sword with no hint in either cutscene that she physically transformed.

It's certainly possible she may have without it being mentioned, but it makes much more sense to me that Mitron's memory is twisted like everything else filtered through him in the whole raid series and the theme of her minions got applied to her as well. He doesn't even get the location completely right and where the actual fight took place from what we see in the Echo doesn't look like the E10 arena.