I've had a chance to peek at chainsaw. Holy points, Batman! Aside from that, you seem comfortable in the style, which is very different style from the Warden story I remember. Impressive range.
Only read the first scene in detail, so I can't justly leave a review.
re the NIT I have reached the insight I was seeking
**************** SPOILER SPACE **********************
I've been comparing the MC to my "evilest good guy". [J e n n a] kills her sister along with her enemies in an elevator. Reviewers were upset, of course. J3nn does it by accident because she hates her enemies. Nit does her evil also by accident because she hates her enemies. The parallels are difficult to ignore.
Where the two characters break pattern is in foreshadowing. It's established in chapter 1 that J3nn has taken lives, and she's consistently evil by nicking things, lying, back-stabbing. That element is not present in the Nit (Her beating up computer mice & answering machines doesn't count - it makes her an angry person but not a murderer).
I shall compare it to Ned Stark. Let's put his approval rating at 80% as-is. If Stark gets angry at something and punches a window or similar inanimate object, his approval rating would probably drop to 79% (This is the equivalent of the mouse). Stark, angry, but in cold, calculating blood, strangles Arya to death. Approval rating plummets.
As a dramatic story, there is a disconnect I can't resolve. If you're going for that, consider foreshadowing it. During the phone call, the sister could mention the family pet MC has killed. Basically make sure not one reader can assign her the good-guy trait. Once a character gets in that slot, the fall from grace really hurts the narrative.
If you're going for any other genre, like noir or crime etc, I wouldn't change a thing - it's perfect as is.
Nb: part of this is I work in technology. I see a lot of people all but hurl mice at walls. I think they're mad that Word deleted their perfect paragraph. I never think they abuse people. If MC would go downstairs, find a car that doesn't belong to her, and smash the headlights and windows, this would have been good foreshadowing. Someone able to break an inanimate object that doesn't belong to them is so far out of the "good person in desperate need of help" slot that the ending resolves well.