Avon and Wiltshire Mental Health Partnership closed the Riverside adolescent mental health unit as a "temporary measure" in February 2024.
But its continued closure means GWH has to do its best to cope with teenagers suffering form psychiatric conditions.
The nurse described how she felt some incidents were not being dealt with seriously enough.
"It is often put to us these children are unwell so in terms of reporting to the police we are made to feel we are doing wrong against the child.
"We are a secure ward and have to buzz people in and out.
"It's restrictions like that and some of the mental health patients we have to remove ligatures such as a hoody they then don't like because we are stopping them from hurting themselves.
"The biggest trouble is we do go up to 18. Most children's wards go to 16. it almost feels like people run scared because it is children."
Another nurse said: "A lot of children are medically fit to go home. No one wants to take them because of their escalating behaviour.
"It has caused a lot of holes in walls, damaged pipes and lots of staff being hit with people being punched in face."
The nurse went on to describe how four registered mental health nurses were unable to restrain one teenage girl who was also verbally abusing staff.
"It is having a massive impact on patients and parents."
She added: "One of my colleagues went off sick as this girl was smacking her head against the wall. The registered mental health nurses were just watching.
The nurse said they have an "assessment unit for children to be assessed" which was then closed. This has left the hospital unit dealing with these cases.
"One teenager was ripping TVs off the wall, she broke a sink. The whole wall has had to be replaced it has ... led to probably at least 15 staff being off sick," the nurse added.
The nurse said that managers had done very little to address the situation apart from introducing a 'safe room' which has not been opened yet.
Another nurse said: "We had a young person who was with us because she had taken an overdose and her behaviour escalated to the point that she was being looked after by three registered mental health agency nurses .
"Her behaviour escalated and she assaulted nurses and security staff. She punched quite a few people."
An NHS report in 2024 highlighted the difficulties of nursing teenagers on hospital wards alongside younger children.
The South West director of the Royal College of Nursing, Susan Masters, said it is a national problem, adding: "This trust (GWH) is the local provision. There isn't another provision anywhere else for these young people to go which is why its very difficult here.
"Children with physical health difficulties, young people with illnesses and procedures need a bright, distracting fun environment.
"Children and young people with mental health distress need the opposite-very calming very sombre. The other issue of course is specialist nursing staff.
"So currently these children are being cared for in an acute unit with children's' nurses that are not necessarily trained in specialist mental health services."
A statement from GWH trust said: "We have individual rooms providing privacy and division between age groups, alongside two dedicated rooms for patients experiencing a mental health crisis.
"Many of the children and young people we care for need specialised care and we are planning to recruit specialist mental health nurses so that we have the expertise to better support children and young people with severe mental health needs.
"It's unacceptable that NHS staff face violence and abuse and we do all we can to keep our staff, patients and visitors safe.
"This is a national issue, however these incidents can be extremely distressing, and we offer a package of mental health support to our staff, which includes de-briefing sessions and counselling services.
"Our Never OK campaign, in partnership with Wiltshire Police, encourages staff to report all incidents and the police regularly visit the hospital and support our own security team."