My Sophie has separation anxiety also. I could have fixed it pretty quickly I think but with her getting so sick I stopped leaving her and working on it sicne stress makes her worse I didn't want to exasperate things. But she is so much better with the separation thing now. As a pup if she were behind the cyclone fence (while I was mowing the back yard) or in a crate (which I only do when I'm painting or on the computer, I have a wire crate set up in the window so she can safely look out while I work but I only put her in when she asks and take her out if she asks it's not for confinement just a window seat)
anyway if I were more than a few feet from her she would fuss and whine and take the wire with her teeth and TUG TUG TUG for all she was worth.
I have worked really hard on it again now that she's feeling a lot better and can walk around the block (I watch what she is doing via NEST camera with my iPhone) and she and Aunt Edna just sit at the window and watch for me. I am usually gone 5-7 min and when I come back I calmly walk in the front door, no eye contact or touching, just go about my business and she's gone from leaping all over me crying like her life was over, to calmly greeting me like it's no big deal.
I work from home so am always with her if I could go back I'd start leaving her from the get go but I had never had a dog with separation anxiety before and didn't recognize it as the big problem it is before it got engrained. My goal is to be able to actually get in the car and go to the grocery store and leave her home and still have a home to come back to.