Okay first off, Christa. When you first meet her in "Long Road Ahead", you can bond with BrOmid. Lee asks BrOmid how they made it. He responds with, "Christa never lets us join groups." In "All that Remains", after BrOmid's death (R.I.P. BrOmid) Clementine can ask Christa during the fire if they could find a group. Christa then says she doesn't trust groups. Why would she lie to Clementine and go against what has kept her alive? Also, Clementine strongly believes she is still alive. We can now rule out Christa. Next, Lilly. Not only has she not been confirmed for Season 2, but Clementine doesn't have any reason whatsoever to believe she is dead. Clementine knows Lilly can handle herself because of her military experience, regardless of being abandoned on the side of the road.