In some ways, it's like the difference between
Ulgu we know, and
Ulgu used for Battle Magic.
Our regular everyday shadow is inquisitive, independent of will, perhaps even capricious, but when it gets a mainline hit of
Ulgu, it twists and turns and lashes out violently, a danger to those around us. Our enemies, so far.
(I don't think we've actually used in much when we're surrounded by friendlies, come to think of it?)
I think it would behoove Mathilde to follow Regimands example and attempt to tame her Shadow.
We might learn something, but in particular before any possible journey to the Chaos Wastes, learning about the previous results of magic (nearly) slipping out of our control might be of value to understand say any weird Wastes-induced effects on our casting.
There's also this.
[Cleric Gunnars: 100.]
...
"You're sure?"
"Entirely. Look," he says, pointing down at your shadow, which as always was wandering freely. "Zhuf-soul. Possession is the same body, same mind, but replaces the soul. Still Zhuf-soul, still her."
Gunnars rockstar introduction, (thankyou Gunnars), but the (natural?) 100 revealed that Gunnars
knows souls.
If he saw in our undisciplined shadow a reflection of Mathilde's soul, does that say anything about her? Could she achieve greater levels of self-control, self-awareness, centering, or similar through mediating on controlling her shadow, and what it means for it to wander freely?