She probably IS really tired (between the demands of pregnancy and the late-night boardroom fighting).
And she's probably dealing with a lot of anger around not getting to do her turnaround. Whether they were working or not, she was surely emotionally invested in her efforts to rebuild Yahoo as a company and now that is being rejected.
It's devastating when you are pouring your heart and soul into something and then the company just kills it and it's beyond your control. I'm sure a lot of us have been through that (I've been through it twice now, at Palm when HP killed webOS, and at Nokia when they announced they were giving up on phones), and I don't think it's any easier at the top level.
Though those eye-watering golden parachutes can't hurt...