I'm pretty curious as to what Blake did exactly that had her all speechless in the face of Roman. Obviously it must've been something bad, if Mr. Wick himself was like 'after what you did...'.

Assuming he didn't hear about it through the grape vine, it might imply Torchwick might have interacted with the fang prior to Blake's betrayal. Maybe the two of them had met previously, thus Blake's deep seated obsession with stopping him.