IIRC she did.

Edit based on your edit: Probably not quite as abruptly as you suggest - usually you need a pattern of underperformance to fire without risking a lawsuit. But Yahoo underwent several rounds of performance-based lawsuits. I think her big mistake there was not cutting once and cutting deep - multiple rounds of layoffs are much more demoralizing than getting rid of all the underperformers at once - but hey, Monday-morning quarterbacking. We aren't the ones at the top making the call.