Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am so sorry to hear about your girl and her worsening symptoms of separation anxiety.
I understand that you adopted her as a young puppy, 8 weeks, but it sounds like has never learned to be left alone and secure in your return. Some adopted dogs suffer from separation anxiety as they have already lost at least one family, including their mother and litter mates.
Most dogs would prefer to spend all their time with their very loved family to make sure that they don't disappear. If she was comfortable in a crate (not destructive) then I would use it while you are gone and at night. Many dogs can come to see a crate as a den. It's a secure place that they can be while the family is gone or when she needs to be alone. She needs to learn that if she goes in her crate you always come back and she is safe. 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.
Since she has already developed negative feeling about her crate and the bathroom perhaps another bathroom or the laundry room instead.
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. 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 and come back for her then she may be able to be out in the house but for now we need to keep her secure and out of trouble.
Ideally while you are working on training her she should only be left for short periods at a time anyway. If you must leave her for longer periods you'll need a friend or dog sitter to come in and check on her, let her out to eliminate and make sure she's OK.
Work on leaving her 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. 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 king ball stuffed with a treat she has to work to get out) to do that she only gets to play with while you are gone.
Leave a radio or TV on for company, initially both while you are home and away and especially at night so that the noise level is the same, home or not. It also blocks family noise at night so she doesn't hear you and get frustrated she cannot be with you while you are training her to sleep and be comfortable away from you.
Make sure that you ignore her for the first several minutes when you get home. 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. In the morning too don't make a big deal greeting her, just let her out and then take her out to eliminate. You can then praise her and give her a treat for that.
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 terriified and extremely anxious then she won't learn to comfortably be alone.
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. If she is panicking she cannot learn, so a short course of medication can be very helpful.
We need to focus on building her confidence in general. A program that may help with that is called "nothing in life is free". This gives her confidence in your fairness and her ability to please you and where she fits in your home. Here is a link that better explains the program: http://k9deb.com/nilif.htm
You also need to work on increasing her self confidence and giving her positive reinforcement from socializing. Obedience class is a wonderful thing. She learns what pleases you, gets rewarded for it and learns to trust you and that if she does what you'd like she is safe and won't get into trouble. She also learns to do this in front of other dogs and people and may make some new friends which will also increase her confidence.
Let me know if you have any further questions.