Tumblr wasn't a bad acquisition. I would also challenge that she ruined Yahoo. Yahoo was already on a downward trajectory with an existential identity crisis. At worst, she couldn't change the direction.
I wonder what Yahoo would look like now if Jerry had accepted the Microsoft acquisition. Yahoo was already in troubled waters at the time, in hindsight it looks like a missed opportunity.
But that's part of doing business. The shareholders and employees (many of whom are also shareholders) might be in a lot better shape had the deal gone through. I'm skeptical that those people are better off with the Verizon deal.
I would like to see your justification for this. Because Yahoo paid 1.1 billion dollars for it and they wrote down pretty much all of the value within a few years. It looks especially bad when compared with Facebook buying Instagram around the same time for about the same price.
You seem like you're more aware of the outcomes of the purchase so I will acquiesce to you, but $1 billion for Tumblr doesn't strike me as particularly egregious. Maybe that's because culturally Tumblr punches above its weight? I don't know.