First, unless you are going to use her for breeding, I'd get her spayed. Also, have you determined with your vet if there's a medical problem? My Scout sprayed, and it was most likely due to two things: a feline UTI, and impacted anal glands.
Does your kitty drag her behind on the floor or carpet? If she does, she most likely has impacted anal glands.
Until you get her checked out, it's hard to say what will work.
In the meantime however, use a good enzyme cleaner like Dumb Cat or Simple Solution to clean up the mess and eliminate the cat urine smell.
Good luck; keep us posted,