I felt the same way, and then I read up on it through a couple of sources. Turns out (as I should have assumed), that the entire Board of Directors voted on and approved the Compaq purchase, not just her. But after it flopped, the Board angled backwards and shoved her forward to take the heat.
It was still a very, very expensive screwup. But it wasn't her alone.
you are correct. and when that happens, the CEO does take the fall.