FWIW, I don't think you are a bad dog owner, I don't think you are a cruel one. I think you care deeply about your dog, but you are at the end of your rope dealing with her nerve shattering behavior. I also think you are a desperate dog owner who is now using a device that is sure to make the problem behavior worse in the long run.
From what I can gather from your post your dog has a pretty bad case of separation anxiety (SA). SA is sort of like a phobia, your dog has an irrational fear that you will not come back, she may also be afraid that something bad will happen to her when she's alone. She panics to get back to you, or to get you to come by her, dogs with bad enough SA have been known to dig through doors, destroy door frames, tear up it's mouth trying to chew out of crates, and jump through closed windows. The dog is not trying to blackmail the owner, they are not trying to tick off the owner, they are simply terrified.
To treat SA you need to slowly work with her to lessen her stress, anxiety, and fear of being alone, just leaving her alone and hoping it gets better is not going to work. Medicine will help but by itself it's not going to help in the long run it'll simply help lower the anxiety and stress to a point where you can work with her. You will have to work with her though. Rather then try and write out what you'll need to do I'll give you some links to some books on the subject that should help you work with her, the books were written by well know dog behaviorist. https://www.amazon.com/Ill-Home-Soon...40_&dpSrc=srch https://www.amazon.com/s/ref=nb_sb_s...=1HCQTSMYWL1R7
This is the forums sticky thread on SA, it has a lot of links that you can check out. https://www.dogforum.com/training-beh...anxiety-29576/
Please stop using the shock collar, I can guarantee it's a band aide that in the long run is making your dog much, much, worse. It's teaching her that she's right to be afraid of being alone, she gets shocked when you are not around and she tries and express how she feels. She may stop barking but that anxiety and fear is going to manifest in other ways, what it's not going to do is lessen, it most likely will get much worse.