Dog with Cushing Disease

I am a veterinarian from Costa Rica and my dog is suffering Cushing' Syndrome. I read in the book "Manual of Natural Veterinary Medicine" by Susan G. Wynn, that Ginkgo biloba is used to manage this condition, using this dose: 1 mg/lb tid or 3 mg/lb daily (dried concentrated extract) or 1 drop/lb bid (alcohol tincture).
I wanted to ask you if this is enough or if I can give her another treatment. I am also using Regurin and Liv 52 (Ayurveda products made by Himalaya Health Care).

As I do not work within an Ayurvedic context, I cannot comment on the formulas Regurin or Liv 52, given Ayurveda and Western Herbalism only share a few herbs in their respective materia medicas. I did however notice on the company's website that Regurin contains Glycyrriza glabra (Liquorice) which can impact adrenal gland function and Liv 52 contains Cichorium intybus (Chicory), a lovely hepatic tonic. I should mention that there is some controversy over the use of Glycyrriza in Cushings. Some authors feel it stimulates adrenal activity thus adding to the problem, others feel that as an adaptogen, it balances adrenal activity. You might want to investigate this controversy further before continuing with the use of Regurin.
As you mention Susan Wynn, I thought I should add that the text "Veterinary Herbal Medicine" (2007) by Susan Wynn and Barbara Fougere, suggests using Ginkgo biloba (Ginkgo) in combination with Carduus marianus (Milk Thistle), Taraxacum officinale (Dandelion root), Rehmannia glutinosa (Rehmannia) and Astragalus membranaceous (Astragalus) for hyperadrenocortism. This formula would have an impact on cerebral circulation, strengthen liver function as well as the immune system and generally build "vital fire" through its adaptogenic properties.
In addition, the use of a good, homemade diet may help as well. Please see the work of Richard Pitcairn, "Natural Health for Dogs and Cats", "The Complete Herbal Handbook for the Dog and Cat" by Juliette de Bairacli Levy and "The Barf Diet" by Ian Billinghurst for further information and recipes. And finally, please pay attention to the amount of stress affecting your dog. Stress, of course, calls upon the adrenal glands to act in all cases of "fear and flight". Given the adrenal glands are already on high alert, any further stress may only do them harm.