I'm sorry to hear you;re going through this with Farrah.
Have they performed any tests to determine what caused the seizures initially? In cats over the age of six it is rarely epilepsy and tends to indicate an underlying medical issue. Considerations would include hyperthyroidism, high blood pressure, a lesion in the central nervous system such as a tumour etc. We do advise blood and urinalysis, a blood pressure check and some diagnostic imaging to determine what is going on.
Given her other symptoms (twitching, hiding, odd behaviour) I would really want to run these tests as certain medical conditions could also cause these signs.
Regardless of the cause, the anti-seizure medicine should help to prevent the seizures. Initially, many cats may be sedate and a little dizzy after starting the medicine but this often improves after a few weeks so hopefully she improve with this shortly.
You mention chronic back twitching and grooming. Have we 100% excluded a flea allergy? This can be tricky to do as you may not see any fleas/parasites but she could be reacting to a single one in the environment. These signs would be typical. Do make sure she has had a strong anti parasite therapy such as Advocate in the last 4 weeks and the home and other pets have also been treated.
Is he skin calm and unbroken? And is her fur short or sparse? We would want to ensure there is no underlying infection or allergy driving this behaviour.