Hello
Sorry to hear this, this is an absolute nightmare.
I have PTSD and had a very mentally ill neighbour in the flat next to me (adjoining walls).
We (myself and all her neighbours) went the route of the police, social work and our local counsellors.
Anytime there was a disturbance one of us would call the police and get a reference number from them. We logged all of our complaints and listed these to the police, social work, local counsellors and housing association (who were letting her her flat).
Every night, there would be about 4 or 5 calls to the police, from different neighbours, at various points during the night.
So, I know how horrible this is.
If you've spoken to them before about it, I would just go the police route. She was very vulnerable (schizophrenic) and I think she was being exploited by some not very nice people.
I've also dealt with druggies in my own stair, previous to that. And a downstairs neighbour who used to play the drums at midnight.
I've lived in my house for 25 years by the way, so that wasn't all in a short space of time...lol!