Have you seen the vet with her to find out if there is an underlying condition? Before I would try any more products, this is what I would do first.
In most dogs, it's caused by a urinary issue like cystitis. The urine actually scalds the vagina and this causes the irritation. In this case, you need to go ahead and see the vet for a urine culture to rule this out and get appriate treatment if you need it (antibiotics, etc).
Urinary incontinance is another common cause of this. If your dog is leaking small amounts of urine, there are therapies and medications that can tighten the urinary sphincter. This will help with the problem if it's the underlying cause.
Other causes might include bacteria, herpes virus, yeast, a reaction to chemicals, shampoos and lotions and even vulvular fold issues.
Before I would use any additional products, I would want to see the vet to rule out any and all of these and then go from there.
Let me know if you want to discuss this more.
