What is the morning routine?
Has anything changed since you were last at work?
Is she otherwise ok? - Does she seem stressed when you leave, or when the dog walker arrives?
In the absence of anything being obviously different, and especially if the rest of her behaviour is as normal, I think my first step would be a check at the vets, just to make sure she's not unwell...
Then I guess play with meal times and see if that helps?