My dog is suddenly struggling with being alone now that I stopped working from home - help?

I worked from home for about two years and during that time my 3-year-old border collie mix Della was totally fine. Never a peep, just slept near my desk all day. Last month I started a new job that's in-office 4 days a week and now she's apparently losing her mind every time I leave.

My neighbor texted me videos of Della barking non-stop for the first hour and a half. She also chewed through the corner of my couch and knocked over her water bowl. I feel terrible because honestly this is partly my fault for letting her get so used to me being around constantly.

Has anyone dealt with a dog developing separation anxiety later in life after being totally fine? How bad can it get and what actually worked for you? I'm wondering if I need a trainer or if I can work through this on my own.