I'm sorry to hear about your mother's difficulty with these ulcers...
Corneal ulcers are dangerous. In many instances, after healing, ulcers can leave scarring that could potentially affect vision permanently. Most ulcers are viral, bacterial or fungal. From your question, I understand that you are dealing with a combination of bacterial and herpes virus ulcers. The treatment options for these two possible diagnosis are quite different. It is possible that your mother needs to be treated for both conditions; however, a fungal etiology cannot be ruled out without proper cultures being obtained. If a fungus is discovered then the treatment is different from what is currently being offered.
I have always told my patients: "If the thought of a needing a second opinion crosses your mind then one should be obtained." Having another doctor's opinion can only help manage the patient more appropiately and allows for a new prespective on a difficult situation. I would encourage you to move foward with a second opinion as soon as possible.
Good Luck and I hope your mother feels better soon...