I don't think Carol is dead. Not sure about the abduction theory, though-- I was assuming that the lurker was the escaped prisoner.
Not possible. All five of the prisoners were with Rick and company killing walkers when Carol was doing her Caesarian.
So whoever was watching her that one time, it's not anyone we know at the prison.
I'm pretty sure that Carol was being watched after Rick chased Andrew (I think that was the name of the prisoner who Rick off and everyone thought was killed) away. I think it was probably too soon for him to be watching and planning on getting the walkers to attack though so it was probably someone from Woodbury...most likely Merle.