Good day everyone and thank you for providing so much information here.
I have uploaded another picture with the main street, side street, etc.
Now so much has come together and such a lively discussion on such a complex topic that I would like to ask again for the sake of accuracy:
What do you think, should we bring all information about the lawyer?
Should we obtain other documents from the municipality or the building authority beforehand, besides the current floor plan?
We have not received a building application from the neighbor or the municipality because the neighbor believes based on her measurements that the construction does not exceed 50m³ and that in Bavaria a building permit is only required from 75m³.
My mother has the purchase contract; we needed it when we had to deal with the new property tax calculation a year ago.
I told my mother that I read on the internet that oral agreements between private individuals can be legally binding and that the neighbor could literally "build" on that, but on the other hand I also read that neighborhood agreements are not legally binding.
Although my mother and the neighbor verbally agreed in my presence, namely: gutter on our property in exchange for cutting the hedge by us several times, they have not yet discussed measurements and dimensions, such as how high, how wide, how long.
Personally, I want to talk to the neighbor again and ask for a construction suspension until next next Thursday, until we have more information from the lawyer, and hope for her understanding (which I think I can persuade her to do, but it is unclear), but I would not know what we could do if the neighbor says: No, I will continue building on Friday. Should we then go to the municipality and the local building authority tomorrow and present the case there, which we would of course inform her about?
What do you think?