Still working on learning about Portia’s London, so I started a map (available here).
In Book 4 she makes her way out to a farm that has recently been burned to the ground. I need it to be in Sheep-farming land, so I picked Sussex county as a location where Southdown sheep grazed. Read more about Sussex county on Wikipedia here.
The Chalk Downlands (also called the South Downs) area seems to be decent farmland for sheep farming.
The Amberley railway station was built in 1923, so she could have taken a train from Victoria station in London to Amberley to get to the Coombs farmhouse. It would have taken about an hour to get there.
For the church in book 6, i’m thinking about All Hallows by the Tower http://www.ahbtt.org.uk/history/