Was Fiona visiting from juvie or did Munsen have her thrown in juvie for merely associating with Coop? If it's the former, what could a nice girl like Fiona have possibly done to get her thrown in juvie in the first place?
She's a perfect girl. I'm sure it's for something she didn't do.
Munsen probably rented the truck, or that's just what type of truck her parents own. If you can accept the security on the house to keep Fiona inside...
Well, who knows, she could very easily be less innocent than she seems. What it was she did though, we don't know. She seems to be an alright kid though, so yeah, she could've been framed also. There's many possibilities.