One of the things she's best at is judging people. She's one of those rare individuals with x-ray vision for character. She can see through any kind of faker almost immediately. Her nickname within YC was the Social Radar, and this special power of hers was critical in making YC what it isA manager at a past job also had a similar "x-ray vision".
During interviews, she would always sit in with another interviewer and never ask any questions of the candidates. She would just observe.
Over 5 years of working with her, every single person she said we should hire turned out great. Every person she said was no good, turned out to not be great.
This was particularly fascinating to watch when she was the lone dissenter either way. e.g. there were times where 7 out of 8 interviewers said "pass", she said "hire" and she was always right.
The first time I read pg's essay about Jessica, it immediately reminded me of my old manager.
It also reminds me of a story from, I believe, Malcolm Gladwell's Blink about the tennis coach who knew before a tennis player served if they would double fault.
Some people have either a natural gift or their brains have picked up a set of weights for their internal neural network that make them fantastic at this kind of thing.