Excessive digging in litter

I know we have had some discussions about litter box digging. I have had both dig a lot and no digging at all. Now Chloe is digging to China and then some. She digs and covers everything, then digs some more. She will leave for a while, then come back and dig some more. Or she might get up on the desk and dig on the desk and the blinds. I didn't notice how much she was doing this until last night. I fell asleep on the recliner and every time I woke up Chloe was in the litter box digging. This went on for hours. When I finally emptied the litter box there sure wasn't much in there.

Anyone have any suggestions? I'm afraid to do much because I surely don't want her to stop using the litter box.

Thanks, Loretta