Calming a Nervous Dog

I have a Shih Tzu dog that is of a nervous disposition, anything out of the normal results in a recurring ulcer problem in her eyes, which we treat with medicated cream from the vets. Can you tell me of a herb that may help "calm" her or where I can go on the web to locate the information?

Although I do not work with animals, I know that Valerian root has been useful in calming dogs, and is used in humans for the same purpose. I suggest a non-alcoholic preparation. The human dosage is 800 mg in capsule form, twice daily, so you can adjust the dosage according to your dog's weight.