Hi sorry to hear about your bitch - if you are wanting to explore all avenues - if this was my bitch i would be asking for refferal to the nearest vet school to a specialist.This way they can do scans and further bloodwork to see what is causing the fits.This would be expensive however if she is insured then that shouldnt be a problem as long as covered.The vets at the referral hospitals are specialists in this field.Good luck and hope your girl is ok.
Dinks