Fiona own her block and her fence, if anyone need to remove it it is that builder that need to come up with a sufficient solution not to affect her daily life.
She has EVERY right not to allow access into her block of land, the fact that she had already agreed the builder to access her land is already a give in and show of good faith to her neighbour.
bring you to court is baselss, that builder is plain arsehole.
what if the tables were turned and she wanted access to build?