Valium is usually only used,temporarily,not an ongoing thing.Having a son(not a dog)I know how serious one seizure after another can be,it is possible(I am no vet)her memoryloss is temporary,but at 15yrs old,who knows,only time can tell.
As for us being rude,you could not be futher from the truth,as was said,you did not mention a vet in your first post.
We do get people with pets deathly ill,believing we can offer a magic cure over the Internet,often the only thing we can suggest is a Vet ASAP.
Good luck with your girl