I was thinking because she's little miss goody two shoes, but I don't think that's the case. Don't see Quinn as the jealous type either, but since I'm not a DIK player, I'm just spouting nonsense. I guess with Quinn, it could be any number of things. Some interactions I've had with Bella and Jill, Quinn was in the background somewhere, usually walking by.
Let me see if I can find the picture of the one I'm thinking of in the library...
There's one during E3 I think as well when the MC's talking to Bella at lunch at the table with Cathy and Jade. Don't know if it means anything. I mean, they're fucking polar opposites of each other.