GND has nothing to do with being pretty or gorgeous. It mostly means that the girl looks like a standard woman.
By that I mean that if you would cross her path on the street or at any other place, like the grocery store, you would never imagine she is in the sex industry.
The term is somewhat the opposite of porn star look. A GND has no collagen lips, no giant fake breasts, does not wear a ton of makeup, Is not tanned to the point you know she spends a lot of time at the salon or has that strange orange Trump look and does not dress in a way that is too sexy for the occasion. She may be dressed in a sexy way, but without crossing the line. You would bring her to the office party and no one would suspect you paid for her company.
She may be pretty, even drop dead gorgeous but it’s not beauty that defines a GND.
One girl that comes to my mind When I think about a GND is Gabrielle Laliberté from Indy Companion or Romie for the Québec city folks. They both are very different, but they would easily go under the radar as SP in a crowd.