how do you define "professional programming experience"?

Getting paid :) Especially for a full-time position with the job title "Software Engineer". I am fudging a bit on the time though, since in high school I was mostly doing troubleshooting IT crap and only got large software projects in the summers.

I guess, getting paid for a programming job, and doing so vast majority (or all) of the time can be considered as professional programming

It would depend on what degree she claimed to have. You could be working full-time and cruise Psychology or Geography, good luck doing that and Mech Eng.