Sadly, her age lends more to the theory that they simply got "other ideas" when they saw her.
Some don't see how it is possible that she wasn't the intended target. Let me give you one possible theory. Keep in mind that I've gone over a lot of theories in my head, including the possibility that Jayme was the target. None of them seem to me to be satisfactory explanations. But here's one that is a possibility:
Say there are two guys who work at the plant where JC worked. Maybe brohters or close friends. (Or it could be just one person, for that matter.) Say one or both were reprimanded or even let go, but in their minds such action was unfair. They feel the company owes them something. Remember, JC supposedly worked that day, and he was in management. But this doesn't even mean it was directly at JC. He might not of had anything to do with the incidents in question. But they see the company as owing them. So they find somebody who is in management. Perhaps they know he has two cars, and they see him as "part of the rich establishment", without really knowing him. So they pick him, and that night in rage break in so get what they feel is owed to them. That would explain why they were there for over 20 minutes. JC puts up a fight. They tell him to shut up, but when Jayme comes out to see what all the commotion is, he gets protective. They are already disappointed not to find anything extremely valuable. So they shoot him. DC manages to dial 911 but they shoot her as well, then disable the phone. So then they ask, pointing at Jayme, "what about her?" One of them gets an idea (which I won't mention here) and says "let's take her and get out of here!" They grab her and go.
I only suggested that maybe they couldn't kill her because she was a child, which even at 13 is possible. After all, SHE isn't connected with the company. SHE'S just a kid. Still, I fear the reason isn't one of hesitation so much as something else entirely...
Please don't read anything into this other than just a theory. We really don't know if this was a lone person, a couple people, or a group of people (which might explain two vehicles, perhaps) that broke in. I'm just throwing out an alternative possibility, that the target wasn't Jayme, but JC, and that even so, it might not have been against JC personally, but against the company he worked for.
I see the incoming tips are dwindling. I sure hope something breaks soon.