Hello and welcome!
Sorry to know the condition of your mother-in-law. Considering her present condition of multiorgan failure there can be several possibilities of seizures in your mother-in-law like hypoglycaemia, electrolyte imbalances, medications and medication withdrawal, bacterial infection, meningitis, uraemia, and hypertensive encephalopathy. Treatment will depend on the cause and is usually symptomatic. Hope she recovers soon.
Good luck and take care!