What has the author Mary Walker written?

There is no widely known author named Mary Walker. It is possible that you are thinking of a different author, or that the author you are thinking of has a different name.

Could you please provide more context or information about the author? For example:

* What genre do they write in?

* What are some of their book titles?

* Do you have any other details about them?

With more information, I can help you find the author you are looking for.