Maybe this is news to you, but engineers typically have to go to college and get a degree before they can work as a software engineer. That typically takes 4 years, starting at age 18, which is when most people graduate high school. A 21-year-old working as an "engineer" at a company is typically an intern.

So to answer your inane question, she wouldn't be an employee because she's not old enough to have graduated college yet. And that's just to get a BS degree; lots of engineers these days (esp. at top-tier companies like Google) get an MS degree before they enter the workforce full-time.

I'm rather appalled that I have to spell this out here on this forum.

Getting a degree is largely unnecessary in the present time, and a substantial volume of people skip that step, especially in large companies like Google that are constantly buying others.