How old is DD?

Start by bullet pointing your concerns down in a notebook or on your phone. Then add extra information where required, this will give you a basis for the email or letter for referral.

When writing to CAMHS just state all your usual contact details and a brief paragraph about why you are concerned. Then bullet point all of your information.

I hope you get some support soon.

In addition, to this paragraph...

Things have really deteriorated. She has multiple marks on her arms that look like cuts but she won’t let me see them. I only glanced them when she came out of the bathroom in a towel, thinking I was still at work. she won’t talk to me about it. When I ask her she cries inconsolably. She frequently talks about not wanting to be here and has panic attacks.

...add details about her age and how long you've been worried about her, how often you're worried, what's the worst it's been, and any ideas you have about stressors or things that are making it worse. Be more specific, if you can, about exactly what she's said when talking about not wanting to be here.

This will help them assess risk and decide how promptly she needs to be seen.

Hope this is helpful.

I've been where you are, except 3 years ago, with my own dd.
We went down the CAHMS route first, took ages to get an appointment then when we did finally get a therapist she was next to useless.
So we went down the private route whilst simultaneously getting the doctor to prescribe anti depressants- incredibly difficult in itself as she was under 18.
She finally turned a corner in Jan this year, and said she no longer wanted to kill herself.
If you can afford it please look into private therapy, it is expensive but the Cahms route takes so long, especially since the pandemic they are utterly swamped.
Sending love x

My eldest DD is a hypnotherapist, please try & get an appt with one for your DD, she helps children like your DD all the time. Obviously still do the CAMHS referral (for what it's worth, sigh.)
My DD does the initial session free to help children just like your DD, she's so passionate about it.

Go to your GP - this is what we did in similar circumstances. It was taken very seriously by the GP and dd was referred to the CAMHS crisis team and seen very quickly. I got her to write down how she was feeling and gave this to the GP when we went in.

Sorry - didn't read properly - get the GP to phone them - they will then phone you to discuss and book in.

Sending much sympathy - it is awful that the school and GP are so useless. I definitely agree it is important to state what it is like at its's worst, that it is an ongoing problem (give details of how long it has been going on for) and also importantly that she is deteriorating.

Give as much detail as you can after that - no matter how upsetting it is. And also when/if you get to the point of speaking to someone don't assume that they have read your referral make sure you go through all the key points with them again.

We had our first assessment meeting quite quickly for CAMHs but then had a real wait to actually start therapy. Therapy has been good but quite a short stint of it after such a long wait. If you can afford private it might well be worth considering but it is very expensive - it was out of reach for us.

I really hope your daughter improves and you are able to get help soon.