Sadly, the amputation of a cat's toes often leads to behavior like you are describing. I'm sorry that your vet didn't warn you of the potential consequences of declawing.
Chances are pretty good that when she was recovering from the amputation, using the litter box was very painful to her feet. She then associated the litter box with pain and also learned that she could potty on the carpet without the pain.
I think you might need to take two approaches to solving the problem. First thing you need to do is help her recover from the trauma of the amputation of her toes. Try giving her Bach's Rescue Remedy daily until she calms down.
Second, buy a whole new litter box, fill it with a completely different kind of unscented litter, and put it (at least temporarily) in a different room from where the current box is. You want to make sure that nothing is the same as with the old box, because she is associating the old box with pain.
In the meantime, get a flourescent blacklight. Use it at night to find all old urine. Treat the urine with an enzymatic cleanser. Loosly cover the spots with sheets of aluminum foil while the enzymatic cleanser dries. Once dry, remove the foil and cover with a thick layer of baking soda. After one week, remove soda and sprinkle with a citrus scented carpet powder or spray with citrus scent. All of this will deter the cat from using the places she has peed upon in the past.
Also, see this old link for other ideas.http://www.thecatsite.com/forums/sho...iate+urination