@PUNKEY,
I agree punkey.
I've lived in a lot of places in the U.S., including the South, and never heard "pretty all"
I've heard "pretty much" all over.
The way I get the exchange, the fact the Olivia is speaking with a teacher, is that she's a child.
Just like a kid will mix up other phrases, I think she said "pretty all true" when she really meant "pretty much all true"
It adds, IMHO a touch of humor to the exchange.