I would assume the episode at the bridge was prior to her exile. Despite Kerillian being, you know, Kerillian, I don’t think she would just murder an entire regiment of Nuln bois as “penance”, when they were presumably just stationed there as guards. I doubt killing random Imperial Soldiers can be considered “making amends”.
We don’t even know if the exile was self-imposed or not. In one of her quotes to Bardin, she explains that it had something to do with “The dead, what else?,” and to Kruber she said she “made a mistake and now has to make amends”.
A mistake involving the dead? Perhaps she, unknowingly, fed a bunch of Wood Elf souls to the Pale Queen, which is why Kerillian is so afraid of her when she’s downed? Or, even worse, fed them to Slaanesh, and that’s why she’s currently on her anti-Forces of Chaos crusade?
Whatever the God, I’ve a feeling that the reason she counts her kills is because she’s counting how many lives she needs to take before it adds up (I’m assuming one Wood Elf is worth at least a thousand Skaven lives).
Or, a bit more of an outlandish theory, she’s counting how many souls she needs in order to bargain them for the Wood Elf souls she unknowingly released prior.
Actually, the latter is good enough reason for her killing those soldiers at the bridge. She certainly seems like the kind of person that would value her own kind above others. Perhaps that’s why she refuses to speak to Saltzpyre about it, because she doesn’t want to reveal that she’s basically trading their souls for the souls of her own kind.
Would also explain why she’s still hanging around with the Stud Squad after all this time, as they would help her collect the souls she needs faster.
Still doesn’t really explain why she’d do a lot of travelling, especially to some Dwarf Hold in the middle of nowhere (perhaps she’s taking revenge for the War of the Beard?), but it would at least explain why she needs to murder stuff.
Oh boy, as if Kerillian wasn’t edgy enough already.