156 years to be precise, with a vampire who is specifically noted to have a spree killing habit during there rulership, who is likely to have being focusing on taking out threats to her rulership such as the Ìce witches and hags due to the immense influence they have on Kislev along with the capability of stopping her as demonstrated by her being eternally frozen by them when overthrown.
Despite her spree killing habits she still ruled a functional state that was capable of resisting the Norse, Kurgan, Beastmen; Trolls, etc.
I think it's likely that she was herself an Ice Witch, and that although the Ice Witches suffered under her rule just as Kislev did, they probably remained part of the state apparatus and military. Khan-Queens need people to rule, and subordinate Ice and Hag Witches ar every useful,
Sure, the Ice Witches eventually turned against them, but from what we know of the revolution in Kislev it was partially motivated by the fact that the younger nobility realised they'd never inherit because their own elders were immortal
Vampires. As many Ice Witches are members of the nobility, I suspect the reason they're currently in a bit of a state is that many of the most powerful Ice Witches had been turned into vampires and were 'killed' by their unturned apprentices/children. What happened in Kislev seems to have been a place couldn't type of revolution rather than a civil war.
Speaking of priests, this might actually be part of the reason why clergy of Tor, Dazh and Ursun has such trouble rebuilding. The institutions that let them take in the boys that would become miracle wielders were annihilated and so all the ones that have shred of potential are forced to leave or killed. Leaving priests through which the gods would have to bruteforce the miracles, if they even wanted to since apparently none of them are worthy.
I don't see why those institutions would have been annihilated. Much more likely to me that they were co-opted by Kattarin and their leadership was purged post-revolution, just as the aristocracy was, given how intertwined they were.
Having it be a case of the vampires taking over existing institutions seems much more interesting to me, and fits with how Lahmians work. They seeks to subvert strengthened human civilisations, not destroy or even conquer them.
I suspect Kattarin even started out with good intentions, and possibly even ruled well for some decades, but became increasingly unhinged as she became older as vampires are prone to, and so responded very badly and counterproductively when younger non-vampiric members of the elite started agitating for more power and authority.