Molly does this too - she hates when I leave the room and because the bottom of my house is open plan she is always with me unless I go upstairs and then she will howl and scream.
Lisa and Tara (from DTI) gave me some drops for her - Dr. Petals Elixirs, Separation Anxiety. You give 8 drops morning and evening. They have really helped to calm her down and she is not as anxious when I leave the room now. I am trying to leave for just a few minutes and come back down if she isn't barking. I was actually able to have a shower by myself the other night!
I hope Minnie calms down for you soon
Molly (Blenheim) & Bella (Tri)
Honey, Cassie & Tiki (Cavalier Angels)