Answer by taking a quote from the following article:

Marissa Ann Mayer (; born May 30, 1975) is an American information technology executive, formerly serving as the president and chief executive officer of Yahoo!, a position she had held starting July 2012. It was announced in January 2017 that she would step down from the company's board upon the sale of Yahoo!'s operating business to Verizon Communications for $4.8 billion. She would not join the newly combined company, now called "Oath," and announced her resignation on June 13, 2017.

After graduating from Stanford, Mayer received 14 job offers, including a teaching job at Carnegie Mellon University and a consulting job at McKinsey & Company. She joined Google in 1999 as employee number 20. She started out writing code and overseeing small teams of engineers, developing and designing Google's search offerings. She became known for her attention to detail, which helped land her a promotion to product manager, and later she became director of consumer web products. She oversaw the layout of Google's well-known, unadorned search homepage. She was also on the three-person team responsible for Google AdWords, which is an advertising platform that allows businesses to show their product to relevant potential customers based on their search terms. AdWords helped deliver 96% of the company's revenue in the first quarter of 2011.  In 2002, Mayer started the Associate Product Manager (APM) program, a Google mentorship initiative to recruit new talents and cultivate them for leadership roles. Each year, Mayer selected a number of junior employees for the two-year program, where they took on extracurricular assignments and intensive evening classes. Notable graduates of the program include Bret Taylor and Justin Rosenstein. In 2005, Mayer became Vice President of Search Products and User Experience. Mayer held key roles in Google Search, Google Images, Google News, Google Maps, Google Books, Google Product Search, Google Toolbar, iGoogle, and Gmail.  Mayer was the vice president of Google Search Products and User Experience until the end of 2010, when she was asked by then-CEO Eric Schmidt to head the Local, Maps, and Location Services. In 2011, she secured Google's acquisition of survey site Zagat for $125 million. While Mayer was working at Google, she taught introductory computer programming at Stanford and mentored students at the East Palo Alto Charter School. She was awarded the Centennial Teaching Award and the Forsythe Award from Stanford.

Did she/does she work for Google?
She joined Google in 1999 as employee number 20.