Taking a gamble on a turnaround CEO is in theory warranted when you have a situation like Yahoo back then (or now), and a "hundred million dollars+" is just the price you pay to get someone who just might have what it takes for a job where they'll both likely fail and have their career seriously curtailed.
There aren't many alternatives for a board of directors when just selling the company isn't much of an option.
A "turnaround CEO" with no CEO or turnaround experience is rich. She is a famous person and that's about the extent of her qualification for a $100m pay package.
Yeah, that's the first place where the "in theory" ran into the hard problems of practice.
On the other hand, in this narrow sub-domain of "high tech", how many turnaround experts are there? Worse, even with the "$100m pay package", how many of them, or just plain CEOs with some experience in with adversary, would be willing to take on the job? Maybe she was about the best they could get.
Hindsight is 20/20, but a boring finance type would have been a much better choice. With the huge Alibaba stake it was a dream position for an MBA type. A pet rock could have been CEO and the stock would have kept up fine because of the BABA shares.
There aren't many alternatives for a board of directors when just selling the company isn't much of an option.