neighbours shed roof leaking

[carr21]

My brick shed is attached to my neighbours brick shed they were built like this when the houses were built in 1980. 2 years ago I had some rain come through the ceiling and was worried as there are electrics in the shed. I called out a roofer and he told me the leak was coming from next doors roof, I contacted her and explained and she refused to do anything. I covered my roof with a waterproof paint and this seemed to have stopped the leak. This week I have seen the leak is back and is running through the beam between my wall and next doors and along midway of my shed which is again causing problems. I was advised my roof and the neighbours should be replaced at the same time so there isn't a joint in the middle else it would most likely leak, she is refusing to replace her side of the roof so what can I do?