A few months ago, her bank sent a man out to talk to her about investments. She ended up buying an annuity, and I don't like it much. If she wants her money back, she has to pay a penalty. She doesn't understand that it's an annuity. There is no doubt that many elderly people face the risk of not understanding complex financial transactions.
Age can bring many unpleasant effects, including memory loss and dementia.
But age does not universally cause mental instability, and the law does not allow us to presume that a person is incapacitated just because of age. A recent case before the Supreme Court of Texas is similar to your situation. In it, a stockbroker assisted an elderly client in transferring several hundred thousand dollars of stock to her nephew. The broker had never met her before, and went to her house so she could sign the transfers. He met with her alone for several hours.