Contentious probate

I need to challenge a positive retrospective statement of capacity based on consistently high scores in mini-mental tests. Mom suffered from vascular senile dementia, probably in the form of Alzheimer's Disease. Also, her symptoms suggest that she had frontal lobe dysfunction. As I understand it, mini-mental tests cannot test frontal lobe dysfunction. I would like to show this via case law where said statement of capacity was found inadmissible on thos grounds. Can you help? Thank you. Tony Clayton (Sheppard)