Ask your vet if she is a good candidate for surgery, and if so I would get her spayed pronto. At this age, she is much more likely to get mammary tumours, and spaying will help slow that down (females spayed before their first heat have an almost zero risk of mammary tumours). Age alone is not reason to dismiss spaying her, if she is in good physical condition. My now 17 year old cat has been under anesthesia once a year for the last four years for dental work, and he does fine with it. As long as you have a good vet and obey the right safety protocols, there's no reason not to.

Females can and will spray, and it often behavioral....but behavioral changes can be caused by medical problems.

I would get a full CBC and blood chemistry panel run, check for thyroid problems and high blood pressure (which can cause dementia-like behaviors in cats), and a urinalysis...for starters.

Nature's Miracle is good stuff, Odoban is another cleaner we used in the kennel that is good on urine odors. I also swear by Equalizer, which is an aerosol cannister and works great on carpets.

You might also try getting a spray bottle of Feliway and using it to spray all the areas where she is currently marking. Sometimes it works and sometimes not. You will need to reapply it every few days.

Urine marking in cats is one of the most frustrating problems to solve. I have one who is mostly good, and every now and then will act up...he's done it in in baskets of clean laundry, on my bookbag, and once we caught him peeing into the toaster! Blech! Good luck, and let us know of anything helps.