My mind is running through the missing elements for A Cornish House. The key one missing is the period of history from which the two women come. They provide Serena with the insight into life beyond her reality. Their stories are vital and where I place them in time makes their stories more poignant.
So I think my mil is speaking from the grave. Bless her. I was waiting for dd in the bath flipping through the rotating bookshelves and I came across A. Rowse's Tudor Cornwall. Could this be the answer? Maybe. I'll let you know when I finish reading the book!