This is exactly what we call as remote symptomatic seizures where seizure-prone brain which is compromised both in its development and function is likely to emit electrical discharges. I would like to know more about her history for the cause of delayed development? about her birth history? is it non-progressive neuro-cognitive delay? CT head has it's own limitations and the best procedure for delineation of the problem is MRI
scan of the brain. To treat or not for this seizures, depend upon the recurrence of seizure pattern and in your child's case, there were 2 attacks after a gap of 16 yrs.. why don't you wait than to start on medications as after all these drugs are commitments on long term basis.