If that was the case she never would have been given the job. That's something any old bean counter could do and they wouldn't require hundreds of millions of dollars for the babysitting job.
She spent Yahoo's money like a drunken sailor, an odd thing to do if her job was managing Alibaba (how exactly do you manage a passive stake in anything?).
Some examples:
* Tumblr - $1.1b with the majority of that later written off because they have only figured out how to keep losing money
* Polyvore - $230m A fashion search engine run by people she used to mentor at Google
* Summly - $30m to a teenager for a news app that was shut down and never heard of again