Separation anxiety is a complex issue with no simple fix. But steps to progress include:
(1) Working on giving her a somewhat private space where she can relax. Examples include a comfy dog bed with blankets, or a kennel with the same. Offer high value treats and toys in this area. Let her know she has a place to retreat and relax even when you are home so she feels less dependent on you being home.
(2) Offer distractions and puzzles for when you are gone. Whether it's a Kong with peanut butter or a cardboard cereal box with crumpled paper and hidden treats (if she won't eat the non-food items!) Giving her things she knows she's allowed to chew on and explore while you're gone can be helpful.
(3) Provide more exercise. A dog that gets a nice run in the morning or other fun activity will be more likely to relax when left alone.
(4) Put a video camera with a microphone in your apartment to better understand at what points she is getting most upset. Is it right after you've left? Then work on leaving for much sorter time periods. Is it when a dog next door or outside started barking? Then try leaving on music or a dog channel TV show to help drown out outside noise.
(5) Do not make a big production of leaving or coming home. If your dog starts getting anxious when you grab your keys then grab your keys before meal time or fun playtime to desensitize. If your dog goes crazy when you come in the door, say "down" sternly and turn your back without any petting or verbal reward until they will sit and then lightly praise them and continue on. If you make coming and going seem like a big deal, then they will become more anxious.
(6) Talk to a trainer! Every dog is different and it tends to be the case that we need to modify our human behavior more often than the dog needs to change.
I've dealt with some mayhem in training fearful fosters in the Philadelphia area. It can take time to modify undesired behavior. Don't panic or give up. Talk to people who can help you brainstorm solutions!
