The reason Sonja is getting on the beds is because they're comfortable, and dogs are great opportunists. You say you don't allow her on the beds except at night - do you mean you allow her on the bed at night? Because if you do, there's no way she's going to understand that during the daytime it's a no-no.
I agree that she doesn't seem to be getting enough exercise. Has she got some chew toys to play with, to keep her busy and keep her from destroying your stuff?
It's kind of alarming that you had a Springer Spaniel that 'ran away'

Did you never manage to track her down again?
Oh, and hope your dogs are OK after the chocolate episode.....