I've never heard the title Ms used in America much at all, especially not compared to use I've heard in several Commonwealth countries. It sticks out at me as being unusual in this thread. But then, even within the US you have big linguistic variations. In Silicon Valley you'll almost never hear anyone addressed as "Ma'am" or "Sir" as that seems too formal, but in the South many people use such titles even in more casual settings with anyone who is their superior or a relative stranger.

Most people I know (which is mainly people from Western states) would refer to her as Marissa Mayer, and the same with any other well-known executive (e.g. Elon Musk, Richard Branson, Sheryl Sandberg, Mark Zuckerberg, etc.) How would you expect her to be named in conversation based on where you're from?