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Think about it from her point of view. She’s nervous. She’s going to find it stressful having a load of banging and crashing and vans parked everywhere and all that. There will probably be a few cracks in her house where your builders bosh in the steels. Your new dormer will look down on to her garden more than before. Etc etc. None of this is fun for her at all. She’s about to have 6 months of light suffering she doesn’t want.
Calling someone a fucking loon for being nervous and deciding to exercise her basic legal right seems a bit uncool to me.
Make a cake, take it round, give her a cuddle.
What works are needed that involve the party wall act?
For anything more than some flashing details, I'd always recommend the adjoining owner appoints their own surveyor. I know party wall surveyors are supposed to be impartial and act for the wall but in reality this isn't often the case.