New Theory: Winston's group gets ambushed by Carver's group. Christa is alive
i was replaying episode for like my 500th time and found out that maybe the guy's who were about to kill Christa may have gotten ambushed by Carver's group or someone else using a rifle.
The proof is in the audio. Both Victor and Ralph are carrying handguns but the shot that can be heard after Clementine starts running comes from a rifle.
Conclusion: Christa is alive.