Taking the cover off the box is the FIRST thing I would try. She needs to be
vet checked for sure. Keep soft crumpled things off the floor, and yes, I'd
add a box. I put an extra in my bedroom on an office mat from Office Depot
and put up a little cheapy "fireplace" screen (wooden) for privacy. People
honestly don't even notice it in there. THey don't use it much but in case
the box is occupado, there is an alternate place to pee. You will notice
that the box was occupied when you caught her yesterday, so, definitely,
there needs to be an extra one.

I'd suggest cleaning very well with an enzymatic cleaner, then with
oxyclean in hot water. That will for sure get rid of all the smell.
Remember, just because you can't smell it, doesn't mean they can't.
Then, spray the affected areas with Feliway. You might also consider
buying a couple of Feliway diffusers. They are expensive, but well worth
it. Here's the lowest price source I've found:
http://www.petguys.com/-039079027910.html
refills are only $12.99 in the same shop.

Have you had a vet check her over for a UTI? If that's not the problem,
then all I can add is to echo what everybody else has said. It can be a
bit of a pain to solve.

Karen,

Here are a few suggestions:

(1) Don't yell.  It may make you feel better, but the cat won't understand
and will probably only associate your actions by fearing or distrusting you.

(2) You said you have been to a vet.  Was Silver checked specifically for
crystals in the urine or UTI?  If not, that should be done immediately.

(3) The general rule of thumb is 1 litter box per cat plus 1 extra, and it's
a good rule.  At a minimum, it is essential to have 2 boxes because many
cats will not use the same box for both urine and feces.  Moreover, cats are
not used to "waiting for their turn" if the other cat already occupies the
box.

(4) Since scratching vigorously (with litter landing outside the box) is a
problem, get a larger box with high sides.  I bought the large-size covered
box (higher sides) and discarded the cover.  That works perfectly with my
twosome.  Also, place a soft rubber mat under the box instead of one with
treads.  The last thing you want is anything that your cats might try to
avoid because it is uncomfortable on their paws.  Soft rubber is ideal
because you can easily pick it up and tilt it into a trash can for cleaning.
Hard rubber will also work, but you would need to vacuum it.  Some people
like to place an extra piece of carpeting under the box instead.

(5) Do you have any of the Feliway plug-in dispensers?  That would be a good
idea if there is any chance of behavioral problems.

(6) Don't use *any* rugs with rubberized backing.  Many of them are natural
attractants to cats, and they will often urinate on the rugs -- and then it
can become difficult to change a bad habit.  If any have already been peed
on, *discard* them and don't count on washing to remove the scent.  Cats can
readily detect scents that the human nose doesn't smell, and a cat will be
drawn back to an object that already has the scent of urine embedded in it.
An enzymatic cleaner should be used on surfaces that surrounded the area
that was used, but I personally would simply get rid of the actual mats.

(7) Avoid using ammonia (or ammonia-based household cleaners) for cleaning.
That mimics the scent of urine and can also cause a cat to pee
inappropriately.

(8) Have you changed the location of the litter boxes?  Shortly after I
adopted Duffy, I tried to move one of the boxes to another location, but he
continued to use the corner where I had previously placed the box.  He won!
I moved the litter box back to the original location, and he happily used it
again.

MaryL

Photos of Duffy and Holly:      >'o'<
http://tinyurl.com/8y54 (Introducing Duffy to Holly)
http://tinyurl.com/8y56 (Duffy and Holly "settle in")