Can the guardian of an adult sell the adult's property after she has passed away?

Recently I received this question from a reader about the powers of an adult guardian. I'm often surprised at how unclear people really are about what authority they have or don't have under legal documents. In this case, I'm glad someone is asking a question! Here's the question and my comments:

"Can my father who was the legal guardian of his mother (passed away from Alzheimer's) sell her