ADHD Diagnosis Evidence through a Right to Choose provider

Hi posting about my 19 year old DD. Looking for anyone who has had an ADHD Assessment and Diagnosis through a right to choose provider on the NHS. My daughter has recently had a diagnosis and she is trialling meds but the only written report/evidence we have is a letter that mentions ADHD Diagnosis at the top but doesn't really say "We have diagnosed DD with ADHD" anywhere on it. I know from past experience with applying for PIP and DSA for ASD that they will want more evidence than that that she has received a diagnosis. So I was wondering what type of written evidence others who had received a diagnosis in a similar way have so I can sense if i'm being unreasonable expecting something a bit more detailed than the single sheet we have. So did you receive a thorough report? Just a letter? Thanks!