Dear friend, welcome to HCM!
It is a complex issue and answer will depend on many things and findings.
Interruption of blood supply to the brain during Aortic cross clamping during aneurysm
surgery may cause ischaemic brain injury
of the brain (if safe to do and feasible) can show if there is any structural damage.
Residual sedation can also cause some dementia
It is best to be guided by the treating doctors about the cause as this a complex phenomenon and they are the best judge for her.
Take care and please keep me informed of your progress.
I hope to have answered your query satisfactorily.