Oh my goodness--thank you for your message. My mother stayed there as a young girl, on vacations from Canada. One night, she was asked to play the piano for Wavertree's guests. She was very nervous but it went off okay. It would be interesting to know if my mother knew your grandmother and sister. I am not sure what the dates would be that she was there. My mother's uncle had something to do with the training of Minoru, the horse which won the Derby, so I would guess it was before WWI.
If only I had asked more questions when my grandmother and mother were still here! A lesson for us all.