Your mother is suffering from dementia .Dementia is the term used where a person has decline in cognitive function( eg memory) that impairs with activity of daily living.Most common causes of dementia are Alzheimer and vascular dementia
next comes mixed dementia.You need to consult neurologist
for detail neurological assesment and higher function test ,to categorize her to which class of dementia she belongs.She requires certain blood test
to rule out reversible dementia.She requires MRI
brain and EEG also.