I'm glad you took her to the vet. Eye ulcers are very painful.
What tear stimulator did your vet prescribe? I didn't have much luck with cyclosporin so Lady's opthamalogist prescribed the new FK506 which has been amazing. I also prefer Genteal Severe eye gel (not the drops) to Lubrithol which are the artificial tears vets usually prescribe.
Apparently, KCS (dry eye) is congenital in Yorkies and tear stimulaters often don't work:
Congenital conditions are often seen in Yorkshire terriers, in which the lacrimal glands do not develop fully and are smaller than normal. In this case, drugs that stimulate tear production do not help, since not much tissue is available to stimulate. Surgery Can Relieve Dogs' Dry Eyes
Since Bella is so young, you might want to consider surgery if tear stimulaters don't work since scar tissue forms over time and will eventually lead to blindness. A salivary gland is moved to the eye and lubricates it. An opthamologist can give you more information.