Thank you for submitting your question. A sudden change in personality can be caused by a small stroke in the temporal lobe. Because the stroke involves only a small area of the brain, motor function( strength, arm/leg movement) is not affected.
A gradual change in personality can be caused by dementia. If she has short-term memory loss, problems with speech( cannot find the right words to express herself), difficulty with familiar tasks, or getting lost in familiar environments, she may have Alzheimer's disease. People with early alzheimer's often show a change in personality.
A head CT scan should be ordered if you suspect she may have had a stroke/early alzheimer's.
I hope this is useful