I just finished season 2 and I have a lot of thoughts but I think the main one is that I don't think Shelby is the mole. Let me explain why I feel this:
1. They made to many references to her taking the red pill that episode and the red pill implying the girls that it wouldn't make sense for that to just change, this show is all about the small details
2. I don't think they would reveal the mole so soon, they like to mislead us, I mean they had Nora and made it seem like Shelby at times well on the island
3. I don't think Shelby would do anything to risk her future with Toni. Yes she wants to stay with her but I don't think she would betray her like that so soon after the boat incident
I could be wrong about the whole thing but I don't think it's Shelby