Totally agree with tiredlady. The thing is when people lose touch with reality, they are not aware of it - that is part of the illness, and that is why someone else has to act on their behalf. I am not a medic but am still trying to recover from a severe episode of depression last Easter (and 3 months on a psych ward) and I am ok for some of the time, but then a blip comes and I feel really down.
I saw people on the psych ward with psychotic type illnesses, where they had lost touch with reality and being treated and I saw some of them get better. One lady who I became friendly with had suffered 2 major episodes of reactive depression, but this time had "tipped over" into a psychotic episode and for the first week I was in there I thought she must have alzheimers as she was very strange, didn't know where she was, trying to take off her clothes, and having to be fed by staff. However she had already been in there for several weeks, and she suddenly seemed to be ok, and was back in touch with reality. She had no memory of the weeks when she had been in a psychotic state. She was discharged before me and was off on holiday to Italy!
I think tiredlady is right - this kind of illness can only get worse without treatment. You say you are scared she would end up on a locked ward, but that may well be where she needs to be (dependent on how ill she is) and the doors are only locked to prevent people on a "section of the Mental Health Act" which means they are not voluntary patients, wondering off and maybe getting run over or some such. I don't think many (if any) psychotic people will agree to going into hospital because they don't believe they are ill, as you say they blame things of what is happening around them. Then for their own wellbeing it is necessary for them to be sectioned under the MH Act for 28 days initially, and this can be extended if necessary. Anyway the doors aren't wooden locked doors if that is what you are visualising - they are glass doors and people come in and out all the time with a swipe card. It certainly doesn't feel like you are locked in.
I think you should try to persaude her to go the GP (and offer to go with her) and if she refuses, you need to see GP or crisis team or CMHT and tell them what is going on with your friend. As others say, they won't discuss her case with you for confidentiality reasons, but they will listen to what you say and should take the appropriate action.
Hoping you get some help for your friend asap.