Shelby's final scene in The Wilds season 2's ending implies she's Gretchen's new person on the inside - the new confederate  

but it's possible the scene is an editing trick. Leah spent her time throughout The Wilds season 1 trying to piece together the mystery of their plane crash and what Nora had to do with it.  

Now in The Wilds season 2, Fatin discovers the truth for herself and brings Shelby into the mix. Every one of them wants to get off the island 

but Shelby struggles with just how much she wants to escape. On one hand, she wants to return home, but on the other 

she doesn't want to lose Toni and face her family. Coupling those feelings with a dream Shelby has of the future, with her, Toni, and Gretchen in it 

At the end of The Wilds season 2, Gretchen rebukes the idea that she would begin phase 3 without having people on the inside. 

The question then becomes, who is the new confederate? Nora could potentially return and reveal that she somehow survived and was taken in by Dawn of Eve, and nursed back to health.  

Then again, all of that could be part of phase 3 - seeing how everyone reacts to a new survival situation, especially if they all know the truth.