A little confused....

Just watched this on Netflix, and overall thought it was decent for an indie flick. I understood what the director was going for by using flashbacks to explain the story and not diving into all aspects of the disease in depth, but there were still a few things I'm confused about, even after rewatching most of it.

1) What exactly happened to this girl that made her this way? I didn't like the scene where she finally comes clean, because she was supposed to be traumatized and speaking in fragments because it made it too difficult to understand.

I understand that she was instiuationalized and killed her grandparents, but I didn't get any other details. (Like who was "Jo" that she refers to trying to help?)

2) Why was the stranger who showed up there? Did she have nefarious reasons for going there in the first place, or did she just try to kidnap her once she realized that the girl may have a cure? Is that the reason why she took her?

3) At the very end, was that dude's wife that he went to kill? It didn't seem like they had left the farm, but who else would they be killing? Or waas that her sister, or the other girl in the pictures? (the jo person she was referring to?)

A large part of the problem with the movie I think came down to poor editing - REALLY poor editing!

Thanks in advance for any answers to my questions.