| Hello,
Although there are several possibilities, 95% of the time, inappropriate urination is caused by urinary infection. Have your vet do a urinalysis. It's a very simple test and all they need do is catch a sample, spin it down, and view it under a microscope. They would also probably do a pH test.
If your cat has a UTI, she associates the pain of urinating with the litter box and so tries to go other places hoping the pain will not be there. If this goes on too long, it might become a habit.
Be very sure she doesn't have crystals in her bladder! They are extremely painful and can scratch the lining of the bladder which can cause the infection. If there are crystals, a diet change is necessary to disolve the crystals to help prevent future re-occurances. Generally Hill's Prescription Diet C/D and/or S/D are good choices. Just make sure you don't feed the S/D for longer than one month. Switch to C/D after one month of S/D to maintain healthy bladder Ph.
People tend to think just because a cat is urinating inappropriately it's a 'behavioral' issue and ignore it.
Kidney failure is a possibility, however, it is low on the list because of age.
Diabetes is a possibility if your cat is overweight. When your vet does the Urinalysis, they can check for glucose in the urine.
Has there been a change of litter or food recently? Are there stray cats hanging around outside? Is there another male cat spraying the outside of your house? Has someone moved in or out? Died? Has there been some incident that upset/scared your cat?
Is she spayed? Unspayed females can urinate inappropriately when they go into heat or smell other females in the area.
I highly recommend switching to a good quality food, if there are no health problems, such as Iams Hairball or Hill's Science Diet. Rule of thumb: The cheaper the food, the worse it is for your cat. Also, don't switch brands, or even flavors, of food very often. Cat's have very delicate digestive/urinary systems and don't take well to food changes of any kind.
Also, most cats don't like scented litter and prefer the scoopable kind. I had a cat who wouldn't use a covered litter box too.
Next to having a urinalysis and/or labwork, my biggest suggestion is that you purchase a Feliway Comfort Zone plug-in! They work miracles! Feliway is made to mimic the phermones that cats naturally produce in their facial glands. It helps them feel calm, happy, and less stressed. If your cat is suffering some emotional imbalance, Feliway could help immensely. I've used it successfully in my own home.
Another thing to help emotional/behavioral issues is Rescue Remedy. It's an herbal/homeopathic remedy which should be given orally (2 - 3 drops on the tongue once daily or placed in the water - if placed in the water, be sure they drink it all in one day).
I hope I've helped shed some light on possible causes for this inappropriate urination. Please get your cat some help! She depends on YOU just as a child would!
As to cleaning the soiled areas: NEVER use ammonia based products. The smell of ammonia makes a cat more likely to urinate in that area again since urine smells a lot like ammonia. Use an enzymatic cleaner such as Nature's Miracle or Anti-Icky-Poo. You can try straight vinegar as well.
Regards, | 
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