Changes in behavior can be because a dog doesn’t feel well or is painful, they are bored or anxious, aren’t sure of where they fit in the family, or are stressed by changes in the social hierarchy or environment/routine. Dogs are pretty simple, they behave a particular way to satisfy a need, whether it be hunger, boredom, fear or anxiety. They aren’t malicious, and if if they show a “guilty look” it is likely an appeasement display in response to our body language and facial expression, which is one of displeasure when we discover that they have eaten the couch.
Dogs have been proven to have evolved to read our facial expressions and body language as way to live peacefully with us.
I think that your girl’s troubles are two-fold.
I think she is bored and stressed and I think that she suffers from separation anxiety from the history I have gathered.
Although you work from home your focus is elsewhere,so she is finding other things to do to keep her busy.
Since you work from home she is very used to having someone home all the time and when you do leave, even for short periods she may panic, and become destructive. Chewing is a great way to relieve anxiety.
Both Boxers and Retrievers are bred to work and be part of a team. While they may enjoy just hanging out with their families and seem lazy, they crave a job and exercise. In modern families that can be running with a family member, playing ball in the back yard or frisbee with the kids. It can be a trip to the dog park to socialize. Agility training or lure training is something they can enjoy too. If there isn’t an assigned task or enough exercise these pups can become a bit neurotic and find their own fun, which is almost always guaranteed to be destructive because dogs relieve anxiety by chewing and digging.
Rescue dogs often have separation anxiety. It makes sense that when they finally find a very beloved family they get very nervous about losing them.
If she is destructive only when you are gone and she does well in a crate (not destructive) then I would use it while you are gone. Many dogs can see a crate as a den. It's a secure place that they can be while the family is gone. She needs to learn that if she goes in her crate you always come back. Sometimes if they are out in the big house alone they just don't know what to do with themselves, get anxious and that can lead to trouble.
If you had a camera on most normal dogs while owners are gone you would see they spend most of their time sleeping. They are pack animals and if their pack members are gone then they rest up waiting for their "pack" to come home and play. In dogs with separation anxiety you will see lots of pacing, seemingly searching and then destructive behavior, either as a way to get out and get to you or simply as a way to decrease anxiety by having something to do. So don't feel guilty about giving her a place she can feel secure in and rest in. In time as she realizes you always come home then she may be able to be out in the house but for now if her crate keeps her secure and out of trouble then let her use it.
If however she is tearing up her crate and is very anxious in it then that's not the way to go. Another option is to use a small bathroom where she cannot get into much trouble while you are gone. You may also want to use her crate while you work if she is getting into trouble even while you are home. I would definitely keep all bedroom doors closed.
If the destruction is only while you are gone we can try to build her confidence at being left alone.
Work on leaving for short periods of time (initially minutes) and always try and make coming and going boring, don't make a huge deal of it as that increases anxiety. Change your routine so that she cannot ramp up her anxiety about your leaving before you've even left. While you are home and have no plans to leave pick up your car keys and walk around the house. Put on your coat and shoes and walk around the house.
Practice her going in and out of her crate and staying there for a few minutes even when you are home. Give her indestructible play things (like a kong ball stuffed with a treat she has to work to get out) to do while you are gone.
Leave a radio or TV on for company, initially both while you are home and away so that the noise level is the same, home or not.
If she wanders off and finds trouble when you are home she’s not allowed out of your sight and if you are busy (working, making dinner) she either comes and sits/lies down in a safe spot you can see her or goes to her crate (when you are bathing children and cannot look away).
Make sure that you ignore her for the first several minutes when you get home from an errand or even when you finsh work. Busy yourself with mail, or putting things away so that coming and going is never a big deal. Once you've been home for a bit then sit down and give her attention. She should be called to you to get attention and she should sit or lie down first. In essence don’t let her behave in an anxious attention seeking manner and get rewarded. She should be rewarded for being calm or behaving politely.
Some of the OTC products for separation anxiety are safe and effective, but they must be used in conjunction with training. Medication alone almost always fails. Here are some links with training ideas that may help you:
As far as over the counter medications I do like DAP products (dog appeasement pheromones) which are synthetic analogs of a calming pheromone a bitch produces while nursing. These come in sprays, collars and diffusors. See this link for information about these products:
See this link for some examples:
I also like products made by Bach's Rescue Remedy: http://www.bachflower.com/Pets.htm
These products must be used in conjunction with training methods. If not they won't work alone. They simply calm her down enough so that she is able to learn. If she is terrified and extremely anxious then she won't learn to comfortably be alone or without you.
If these aren't enough I would discuss medications, such as Clonicalm or amitriptyline, with your veterinarian. She is fairly young and they likely won't need to be forever, just until she learns to trust that you are coming back and it is OK for her to be alone in her safe place. I do not see her as a dog that needs medications yet, but I want you to be aware that they are available if things really go awry.
A program called “Nothing in Life is Free” can be a lifesaver for anxious dogs. It trains them that their calm behavior and following the rules leads to positive outcomes and that you are reliable. Here’s a link that explains the program much better than I can. I use it with my very neurotic, separation anxiety stricken rescue greyhound and it works very well.
Please let me know if I need to clarify anything, or this leads to more questions.