From an article I found:
ENTERTAINMENT WEEKLY: I have to say, I was shocked to see Sandra quit immediately after arriving to the Edge of Extinction. What was behind her decision, and what sort of impact does this have on her Survivor legacy?
JEFF PROBST: I’m surprised that you were shocked. We named the challenge sit-out bench the “Sandra bench!” There was 0.0 chance that Sandra was going to win a challenge against the group of players already assembled on the Edge. We all know that Sandra does what Sandra wants, and Sandra wanted to go home. I don’t think it changes her legacy in any way. Sandra is a legend. She is connected to so many iconic Survivor moments.
When we are casting new players, Sandra is often referenced as an inspiration for why people want to play because she showed you could win this game even if you’re not a physical player. And Sandra did one other thing for the past 16 years… she said yes every single time we called. I wouldn’t even get the words out and she would say, “YES! Whatever it is, YES!” I’m not exaggerating. She had no idea what we were going to ask, she didn’t care. She always said, “Survivor has been good to me, and I’ll be here whenever you need me.” So after 16 years, if Sandra is done, I’m good with that. Goodbye to a true one-name Survivor icon.