Yahoo was a capsized ship before Marissa came aboard. The fact that she got it into harbor at all is impressive enough for me. I always assumed there was a near-zero chance that she would save it from complete collapse.
Making bets that don't pay off is par for the course for a CEO (Bezos & Satya are both great at this), some just have the luxury of huge profit centers to point at when investors come knocking. Marissa made her bets — some worked, others didn't. She managed to get an asset that, for a time, was negatively valued in the market[1] sold for parts. How she is compensated for the feat is, I assume, based on her employer's evaluation of that result.
1. http://www.investopedia.com/stock-analysis/070215/why-yahoos...