"More spoilers- And was the betrayal that she was in there doing community service and wasn't volunteering or that she had created the website for the play she was writing and was already taking the steps to produce it outside of the prison?"
Well, the easy answer is that the betrayal is that she was stealing their stories without permission or compensation. And she also jeopardized their standing (particularly Walter's) with the parole board. And as they emphasized time and time again (through events that we now have to see as fictionalized) she disregarded the rule that WHITRIPSITRIP.
But now that I think about it, it's an interesting question. She never says whether she's doing community service or volunteering. Jeremy assumes it and she doesn't contradict him. It's also interesting when you go back and think of the line the dance teacher had about the men knowing which of the volunteers are there for the long term. They let themselves be vulnerable by showing their anger on making the "discovery" but also put in an earlier line that's foreshadowing but also kind of saving face.
Another thing I thought the first time was that all the stories came across as too polished (you're supposed to believe that when they tell them in context, Bey, Jeremy, Sunnyside, Source, etc. are telling those stories for the first time after Dep. King told them to write something) but that makes more sense if you don't think about it happening in real time but as a play they wrote to reflect their experience and tell their stories.