OK, so when she is left alone, there are 2 other cats for company. But, given that there are 2 other cats in the house, could she be establishing a territory, in the most inappropriate of places? If a cat doesn't cover its business, it is deliberately trying to leave a smell as a signal to other cats. Is this dominant behaviour?
I still think that the solution could be to isolate her, or at least shut her firmly out of the kitchen, when you are not around, until she learns appropriate toilet habits.