She saw no way to get her power back, so fuck it: toss some chaos at the board, wipe some of the players out if possible, and see if you can scrape your way back to the top after the fallout.

It's obviously not a good plan, and she's nowhere near as smart as Littlefinger... but she's a desperate character losing her family connections at nearly an exponential rate. It makes sense that she would act on short-term gains. That's always sort of been her MO anyway-- I feel like the show has had several scenes in which characters explain to her that she needs to play the long game better, and she just smirks and tosses their opinions out.