What about getting her used to a crate for when you have to leave her by herself so then she is not shredding things when you are not there. The behaviour will stop in time, I'm sure, but it is going to be very hard work for you! I've had lots of labradors over the years and they can be some of the most destructive dogs around, but usually by the time they were two, they had settled down. (Is this why she was in a rescue home to start with?) But, as Lankeela says, you must find out where she is getting out and put a stop to that. Good luck, and I hope that you have lots of good times with her.