Ok can't find the code of conduct but they are definitely not apart of the university it's self as they are all over the country
Lecturer and former Head of Department & University Senator here: your DD is doing the right thing by consulting with her Personal Tutor, the University welfare/wellbeing service. She should also be in touch with the Welfare Officer of her Students' Union or Guild.
Her Department will be able to do very little, although her Personal Tutor can signpost the appropriate services who can help her. She might also discuss with her tutors the impact of this on her university work - see them now so that if she finds anything further happens, or there's an impact on her ability to submit assessments or perform in exams, there is a back story and shows she taking action to help herself.
As the accommodation is privately run, there is actually VERY little the University can do, except maybe help your DD liaise with the private Halls management.
She should of course go straight to the Hall's management and ask to be moved. Indeed, I"m surprised that the halls haven't removed Student A as I'm sure his behaviour has breached their regulations.
From what you say, there's a case for the University to see Student A on disciplinary grounds. But there's a real problem for all university staff in this - I have found myself in this crux several times.
While my ethic is "I believe her" we live in a society where everyone (even with obvious evidence) is innocent until proven guilty. So the University has to go through its published regulations and procedures in any action against Student A.
If you go to your DD's University website and get past all the annoying advertising gff aimed at Lower 6th formers for Open DAys, you should be able to dig into the actual working doscuments of the University. These are public documents and there will be a whole section about student behaviour and what procedures are to be taken when there is an allegation of misbehaviour.
However, universities are not the police nor the courts. It sounds like Student A needs to be charged by the visitor who suffered personal injuries. It's gone beyond the usual things we hear on Senate misdemeanour/disciplinary hearings (although I could go on for hours about the shocking level of cheating rife by undergrads).