cat cant forget the fleas

how can i get my cat to realize there are no more fleas in the house she sits on the bureau all day and night

Your cat is probably well aware of the fact that there are no more fleas.
   
The bureau is now the cat's preferred hang out and that's that.
   
It could be worse. We had a Maine coon who insisted on sitting on top of the TV and hanging his monstrous tail in front of the screen.
   
He never seemed to miss a hockey game, hopping up on the TV and dropping his tail, to the chargin of a houseful of hockey fans.
   
The same cat also loved the top of the microwave. We were probably the only family in America who had to move a 23 lb. cat every time we wanted to nuke popcorn.