Your sister having meningitis
at 5 years of age probably doesnt have much to do with her current problems. The cognitive deficits that you have explained along with some imaging findings suggest that she could be having an organic disease of the brain, probably an infarct. IN that case things should improve in some days and she should be started on proper prophylactic treatment like clopidogril, aspirin
and antihypertensives. Piractem and memantine may also help her.
Thanks for posting a query at HCM. Hope she gets well soon.