I think part of the problem is that I haven't written a romance as such, unless you count the love affair various characters individually have with either the Carsingthorpe Estate of Carsingthorpe Lodge, which brings me back to my original one-line summary:
Three women from different generations, each in love with the same house.
Although strictly speaking Linda and Julia aren't quite from separate generations, they do represent the different outlooks generated by being born before and after the outbreak of World War II. So, I think for the synopsis I need to build on that framework and show how the three women have dealt with similar situations and how Linda applies what she learns from the lives of the other two to move on with her own life.
[ETA:] I've started a spreadsheet laying out each chapter scene by scene, and I'm also hoping this week's bloghop will help give me more ideas on what I need to emphasise about the world of my saga.