Hi Jm,
I'm sorry to hear that you're having such a bad time with this beloved snake of yours. That really sucks!

Fortunately, I haven't ever had this problem with either of my SDs yet (knock on wood!), but from what I understand it's a fairly common issue with Retics. I'm sure you've already experimented with everything regarding cage size, temperatures, humidity, prey size and feeding schedules, yeah? And, as has already been mentioned, the desire to breed can also cause them to push, but she shouldn't be sexually mature for 2 - 3 more years, should she? My male is definitely extremely active (and destructive) in his enclosure. I can't keep his tub dry (he's still in a 41 qt. rack), because for some reason the little stinker insists on keeping it soak and wet with the water from his water dish. From what I understand, cage destruction is also pretty common with Retics. Since Retics are such energetic, inquisitive and intelligent animals I have to wonder if it couldn't simply be boredom/desire to be handled that might cause them to push and/or destroy their cages? My boy especially is very sociable and LOVES being out and being handled! How often do you take your girl out and for how long?
I would highly recommend contacting Garrett Hartle of Reach Out Reptiles here in Pittsburgh. He specializes in SD Retics (exclusively) and seems to be one of the authorities on them these days. He's very friendly and helpful and i'm sure he would be happy to share his experience with you.
With regards to building your new enclosures, i'm curious why you wouldn't want to use PVC board instead of birch?