We have a mal-a-ket solution from the vet to cleanse the area - and she gets a bath once a week w/ a chlorhexiderm 4% shampoo from her dermatologist.
When you say change her diet are you thinking food allergies? She has allot of environmental allergies and gets and allergy injection every 3 weeks. The elimination diet didn't turn up any food allergies - but we did that @ 7 years ago - so things certainly could have changed...
The smell isn't coming from the vulva it's coming from the anus. Does seem less intense/strong since we started treatment - but the overgrowth of bacteria is on the anus and tail as well.
The vet said that given the sx she really didn't think it was a bladder infection and felt it was a more localized infection.
FWIW - a couple of members on a different forum - who I believe are experienced breeders - told me the cysto was a routine procedure - and from what I have since read - the best/only way to accurately diagnose a UTI/bladder infection. So I learned something. I still don't like it - only because I don't trust people to be competent and any time you perform an invasive procedure you open the opportunity to introduce human error - but that's just me and my paranoia.