Protecting parents from making unsafe decisions is a difficult challenge. As long as an adult is competent, they have the right to make poor decisions. The only way to legally
prevent this is to have the parent declared incompetent in a court. Of course, unless you move your mother into full time care, she could still get up in the middle of the night and pour sand on the driveway. I'd advise against legal action.
A good first step is have your mother assessed by a psychiatrist who specializes in older adults. If your mother has a history of impulsive, unreasonable behavior, she could have a pre-existing personality disorder. These usually do not respond well to medication. If the actions you are describing are more recent, she may have a neurodegenerative brain disorder that may improve with treatment.
An important step is to remove yourself as your mother's conscience. It is not your job to tell your mother what she can or cannot do. After all, she raised you to recognize reasonable behavior! All behavior is purposeful. She may be attention seeking, or her behavior may have been part of a marital game with her husband; you know, I'll do it before you do and then you'll never hear the end of it. In any case, it is not part of your role as a caregiver to reprimand her.
I benefitted from reading the book, Dance of Intimacy, by H. Lerner. She discusses how relationships are like a dance; when you change the step, your partner has to change also. I suggest that you try a new way of relating to your mother, which is to ignore her unreasonable behavior. Perhaps ask her if she thought sanding the driveway at 2 AM the day after surgery was a wise course of action, and then leave the topic. To be drawn into a discussion with her would be to join her craziness.
It probably was helpful to her doctor to know that any complications to the surgical site would be due to your mother's actions rather than an medical error. There was no need to tell your mother that you were going to tattle. Decide on the right course of action and do it. When you tell her what you are going to do, it may be preceived as a threat or a dare. Remember that the person who will suffer the consequences of a longer recuperation period is your mother, not you.
You already know that there is nothing the adult children can say or do to improve her behavior. So act on that knowledge. Do and say nothing in response to her unwise courses of action. Be available to help if needed, or not. Your behavior, your responses to her unreasonable actions, are your business, not hers.