Help me diagnose my dog (very strange symtoms)?

i have a 6 year old dachshund that is very very sick. it started with a swollen throat eariler this summer, then glaucoma which led to blindness, a strange cough. she was coping with the blindness, getting around without too much of a problem. then it seemed like she couldnt balance well, falling over alot. it is very sad. i have taken her to several vets, she has had tests done and been given meds for symptoms but no cure. the only thing i can think of is brain cancer? or some infection of all her systems?