To get rid of the smell-
I see you are in the UK, I am also, for pee accidents I use Simple soloution urine, spray etc remover. Its not too bad-a-price but it is excellent, has a nice smell, and really does work. Make sure you follow the directions and let it soak right in.
Next if you havent already you need to get the cat to the vet to check for a uranary tract infection, as peeing like this is a sign of it.
please let us know how it goes.
(btw where in the south west r u???? im also in the south west )
using a white vinegar also works very well for cat urine
some articles say to use a 50/50 mixture of the white vinegar and water, i just use it straight up. either way use it in a spray bottle to squirt the carpet after you have cleaned the urine. also since im sure it has seeped into your carpet padding use a hypodermic needle (should be able to get from your vet or local farm supply store) and inject small amounts into the carpet padding beneath the carpet. this part you will have to do repeatidly as you dont want to over saturate the carpet. it works very well and is very inexpensive especially compared to other enzyme cleaners!! good luck!
If the urine has really soaked the carpet you may need to get rid of it.
But the main thing is, why is she doing this? The two most common reasons are: the box is too dirty, or she has a urinary tract infection. She needs to be checked by the vet. For more ideas on solving the problem, please see the articles on Litterbox Secrets here: http://www.littlebigcat.com/index.php?action=library