Here's a different scenario. Not saying I think this is what happened, but I could see it as a possibility:
Jayme is home during the shootings, but gets away. However, she's seen enough that she understands what happened and is scared--really scared, because the crime was committed by someone she doesn't think she can get away from. If she tells the police, maybe no one will believe her so she runs. If a 13 year old girl won't go to the police, can't trust her family and doesn't know her neighbors the most likely place to run would be a friend's house. 13 year old girls are notorious for keeping secrets from their parents. I can imagine successfully hiding a friend for a day or two from my parents when I was 13. I can even imagine some situations where a friend's parents might help harbor her for a while figuring out what to do. I know she's been gone a scary long time if someone abducted her, but 1 or 2 days isn't that long to keep a secret.
If Jayme did run, the person she ran to might have to be close enough to get to on foot -- If she called them on her cell phone no doubt LE would know that by now. I've been in northern Wisconsin before near Cranberry Lake and remember it being darn near impossible to get a cell signal sometimes. But can't remember if there were still payphones around as a result. If there are I hope LE is checking all calls made from a pay phone within the radius a 13 year old girl could get to on foot.
Another perhaps even less likely situation is that an adult close to Jayme felt she was in danger at home, and killed her parents and took Jayme in order to "protect" her. Doesn't mean that the parents were really a threat--in this scenario the abductor could be a delusional crackpot.
Again, I don't think the odds of either scenario are particularly good, but I'm holding out hope that's what happened because I think they're the best hope we have that she's unharmed.