Feel for you. My DS1 was involved with MH services 2/3 years ago - (not CAHMS, he might have been too old for that) and I was caught between data protection (he's over 18, can't tell you a thing) and, eventually, a referral to SS on grounds that he was hurting younger DS. I had gone, with DS 1, for support and practical help and ended up embroiled with SS in a tangle of nonsense which we have only recently managed to unravel and get free of.
DS1 still has MH problems - long story.
But you - yes, back then GP (much persuasion) made referral to psychiatrist, though he was working for this bunch of tossers in the MH clinic.
And, yes, SS involved without my being forewarned.
And, yes, once DS1 ended up in hospital, his psychotherapist said to me on the phone that she was 'curious' why I hadn't tried to get in contact with DS before now. He had left home and I had had the devil of a job trying to track him down - till eventually I did to the MH hospital. I'd left no stone unturned and yet she said this. Other times, I was accused of being too inquisitive - asking too many questions, wanting to give his new carers information, wanting to contact him .... It was horrible.
Thoughts ... on the SS front, Family Rights Groups proved a wonderful source of positive encouragement and practical help: www.frg.org.uk/ Free phone helpline worth contacting on Monday.
If GP will now refer directly, could you try another or go through choose and book, if that still runs. This would be a referral like any other, surely. For psychiatrist specialisms/interests, try Dr Fosters on-line guide.
It's exhausting dealing with the MH services' many problems and inadequacies. Could you hand much of it over to PALS? Your NHS mental health trust should have a PALS service and if you're lucky, they'll be OK or moderately OK. Yes, it's the first step of a complaint but better than that, it can set balls rolling and a good PALS service will act as a conduit between you and the professionals.
Have you phoned Young Mind for their take on this?
Hope all goes well for you and DD.