Hershee is adorable and lucky to have you,as you are lucky to have her.
They do, however, get vestibular syndrome which *looks* like a stroke when it becomes acute and causes nystagmus, vertigo, limb weakness, instability and falling down.
It's very common in older dogs.
Has your vet ever -really- checked her ears?
http://suite101.com/article/what-is-canine-vestibular-syndrome-a51752
Please check into it.
There may be treatments that can improve her quality of life.
I lost my beloved Minny to it because my vet wouldn't listen to me when I told him she hadn't ‘had a stroke’ and didn't have ‘epilepsy’.
By the time another vet listened, it was too late.
I grieved -hard- for 2 years and then “just deeply” for another 10.
Good luck!