Inertia and Identity. She’s been a Republican since she was 18 (according to the article), so she has identified as a Republican during all that time. To renege on that identity probably feels like being duped by the party and people in general tend to resist accepting that that they screwed up/made a mistake.
It’s more palatable if they can point to reasons that the party left them and make them feel better about severing those ties. It’s the same reason people often delude themselves into staying in an abusive relationship. If they accept the situation is FUBAR, they might feel like they should take some of the blame for being a part of it.
Trump and Kavanaugh offer a visceral representation of some of the most egregious aspects of the Party’s rotten core, so she can point to them and say, “It’s not me, it’s you,” and still hold onto that identity she’s built for herself. If that’s what it takes for her, I’m not willing to hold it against her now that she’s made it there. More need to follow to finish off the GOP once and for all.