>>149754813
My assumption is mostly the same; in that she sees this grand adventure between her friends and realizes that she wasn't...really a part of it. At all. She didn't even get a gem. And it makes her realize that she doesn't even fit in with the trio either, and she's certainly not happy just hanging around and being this quiet wallflower. So she moves on to make her own friends.
I think it's a nice contrast to Darrel, who shouldered his way into the story and refused to leave it, to its detriment. Darla is someone in the story who didn't need to be there; she has her own stories to make.