Y’know I went looking for an old post where I explained why I bought her getting vicious with Howard, but turns out I was replying to you, so I guess you have already seen my argument 
.
Fair enough if it doesn’t work for you, really. But for me this is a case where the character development does feel more natural than forced. If it were anyone else, some innocent, I might balk. But Kim has a plethora of reasons for very specifically hating Howard, a strong financial incentive to screw him over, and years of Jimmy’s well-meaning but de facto malevolent influence slowly eroding her moral fiber. From lying to her ignorant pro bono client to get him to do the right thing and plea out, to screwing her own corporate client to play Robin Hood for the little man, Kim has very slowly broken bad in a believable way. For me 
.
She’s still well-meaning, but her morality is now tied entirely to saving her destitute clients. Professionalism and respect for the corporate world is out the window. I think she absolutely has grown to loath Howard and if she does in the future screw over some innocent as “acceptable” collateral damage after this I will probably find that believable as well, as corruption of the soul can indeed be a slippery slope.