cat eliminating on carpet

Question
Hi,
I have 2 cats, one is a diabetic.  He urinates a LOT, so I got a Smart cat box, which uses safflower seeds that repel liquid and collects the urine in a reservoir.  My other cat was not crazy about this litter at first and I had to put layers of regular litter over the seeds and gradually reduce this until she was using it without problems (although would occasionally pee in the bathroom sink).  Recently I was very ill for a week and unable to tend to the litter box and the urine reservoir overflowed onto the floor.  Since then she has not wanted to use it and has been going to the bathroom on the carpet in the bedroom and the office (I keep the office closed and now she goes in the same spot in the bedroom).  I have tried the layers of litter trick to no avail.  I put out a regular litter box and she did use that but my other cat did too, and he pees so much that the odor becomes intolerable in a day, and then she won't use it because of that.  How do I get her to stop going on the floor and use the smart box again?  I will be leaving for a week and my friend will be petsitting so we would like to know the best way to treat the area, and will be leaving the bedroom closed, but we do not want her to find another spot to start going in.  I do not want to give her up or anything else but I am at my wits end.  With the other cat's diabetes and amount of urination a regular litter box is simply not an option.  Do you have any suggestions?  
Thank you very much in advance.

Answer
Margaret,

Some cats are VERY particular. I would start with a fresh larger litter box and deep litter using a clumping cat litter like Tidy Cat or Fresh Step. You can scoop out the clumps when you see them, and there isn't any odor.

You may have to scratch the Smart box for awhile, maybe forever. Cats are creatures of association and experience, and if he has had a bad experience with the Smart box he will remember it and probably avoid it.

I would suggest putting a couple of boxes in different areas too.

Tabbi