Concerning Jenna
Even when I met her at Rivington for the first time, I was sure this had to be an Orin spy. So I also refused her, but she came anyway. Then I attacked and smashed her skull in camp, but she was unkillable. Then I ignored her, and nothing happened...

Turns out she's the "falllback option" for Orin's hostage. If none of the eligible camp members can be abducted, then Jenna is taken, so for that reason she must be there.