Exactly She was there not because she wanted to clear her husband's name which they have now besmirched and to restore his clean, war hero "legitimate" businessman and "public benefactor" reputation but as the dutiful wife which no doubt helped his image as a family man and respected businessman

Kay knew that Michael had become a man like his "Underworld Chief" father
No doubt she was disgruntled and disillusioned because the crime proceeds blood money laundering is not “completely legitimate

And then, bang! The bullets started flying and jolted Kay into reality, the denial and delusions no longer holding up
However I am still not convinced she made her decision to leave right after the Tahoe shooting?

I reckon, it could have started off "It never ends...," but listening to all those heinous, horrendous things being said about her evil husband, he not only ordered murders but had personally committed murders himself triggered the final nail in the coffin