You know your mum is at the end of her tether, but do you think she puts on a stoical face when seeing the CPN etc? I think a lot of people do, and it is only by showing the case workers just how bad the situation is the right help is made available.
The pen and paper approach is a good idea, so why don't you get your mum to unburden herself to you, and to tell you all the things that are difficult for her, day by day, so you can present a sort of diary to the CPN showing just how bad things are. Written reports do make it into patient's files, and I know our CPN finds it useful. Otherwise, when you see the CPN if the only thing you can say is 'he's been very difficult' without chapter and verse about how on Monday he was threatened by people with guns, on Tuesday he said or did this, on Wednesday he was ok but on Thursday the gunmen returned, it is hard for the professionals to assess just what is going on. Even if you can't see the CPN yourself due to work commitments, you should be able to speak to him/her and send your report.
On a slightly different note, our CPN is no longer allowed to e mail me for some sort of confidentially reasons - has to telephone, which is tricky if husband is in earshot. However, there is nothing to stop me emailing her, so if I have concerns I still can send stuff (again, much easier than having the possibility of being overheard describing a problem, which would usually lead to denials and arguments).