Separation Anxiety? How do we overcome it?

At first I thought maybe it was just nerves from being away mom and siblings the first night or two. But I'm starting to think it's not.

I cannot leave the room. I cannot walk away from her pen. I cannot turn my back or ignore her. I can't move.

If I do any of that she starts pacing, crying, barking, and/or howling. I cannot even get her to a baseline because if I don't even pay attention that upsets her. I reward her with a calm "good girl" and a pet and/or treat when she quiets down. But it's short lived ALWAYS. I'm at my wits end, so is my fiancé, I can't do anything without this behavior. What doesn't help is my upstairs neighbors are less than happy about the screaming...and for some reason they're home all day after working 36-40 hrs a week previously? So there isn't a day they aren't home.

She is going to doggy day care with a local sitter who only takes 1-2 dogs depending. We're also starting classes with her this weekend. She has snuffle mats, slow feeders, high value chews, puzzles, and we do clicker training every time she's awake for 20-30 mins. Plus a 20-30 min walk (with leash training which is why it takes so long). She'll nap. But if I move, I wake her up and rinse and repeat this nightmare.

I'm a wreck.