Anxiety Issues

My husband and I rescued a Cataholua/Australian Cattle Dog mix about 2 months ago, named Zoe. When we are around she is the perfect dog: smart, easy to train, doesn't bark, housetrained, friendly with other dogs and people and loves hanging out in her crate. Unfortunately, when we leave she flips out. She will bark and howl for a long time and more disturbing, she chews on her crate to the point I worry about her hurting herself. She actually chewed a hole through her plastic crate, so we have switched to a wire one. She has now chewed through the plastic pan at the bottom of this one as well.

We have done a lot of training with her on this, like leaving for very short amounts of time (which we have built up without issues to 30 minutes), giving her a lot of exercise before we leave, etc. I should also say that we are only leaving her for about 2-3 hours, and leave her with her favorite chewing toys, which she totally ignores when we are gone and just goes for the crate.

I'm worried she is going to hurt her teeth and paws with the chewing. Any suggestions on how to ease her anxiety would be greatly appreciated!