Answer:
Alzheimer's
Step-by-step explanation:
Margaret's condition starts with tiny things and worsens over time, a key symptom. Also, her memory is going away and her motor coordination skills are lacking, which means she's forgetting how to do simple things. You mention that it happens around her 70th birthday, and Alzheimer's most often starts in old age.
*If you need more info, you can see the BrainPOP video on Alzheimer's.