I think Mathilde might have a moment where she can feel the other shoe drop. Grey Wizards are occasionally called upon to do things that are ugly but necessary, and deep down she may have had the feeling that it had been a long time since she had to do something that actually made her uncomfortable like that, that pushed her out of her comfort zone.
It's not like the Alric/Alberich thing or the Drycha thing, where she started out doing a favor to someone and then came out of it having averted a crisis while also enriching herself without guilt. It's not like the "Bird started monologuing at us" thing, where we assuaged ourselves of guilt by giving most of the truth to Belegar and Algard.
This is something actively unpleasant that we are choosing to do. It is getting involved into something ugly and political and very high-stakes because if we don't, more might suffer. Vladimir might not deserve death, there is no crime he appears to have committed save negligence and inaction, but certainly, neither would the innocents of Kislev deserve death if the nation doesn't start preparing right now. It is something that we'll have to take to our grave, one more secret that would explode into war if it gets out or we botch it.
In short, it's entirely within the Grey Order's wheelhouse. So I'd agree that Mathilde would feel confidence in doing this. A grim confidence, but confidence regardless.