Ok, I have now read the thread and do feel it is likely that your daughter is missing some sort of diagnosis. I can see that several have mentioned autism and dyspraxia, which I can also see as possibilities.
I just wanted to offer something else for you to consider, as I dont think anyone else has mentioned it - learning disability. Note, this is different to learning difficulties (e.g dyslexia). Learning disability is a lifelong condition that starts before adulthood and affects development. I work with adults who have LD, many of whom also have co-occuring conditions e.g Autism, ADHD. Like with autism, there is very much a spectrum to learning disability.
I work with adults who have mild LD (in my experience very much a hidden disability, you would walk past them and not realise that they have a disability) as well as adults who have profound LD and require 24 hour care. LD affects everyone I work with in different ways, their needs and things they struggle with are all so different.
You have mentioned that your daughter has complex medical needs and I know that a cause of LD can be difficulties in birth and childhood illnesses/accidents/injuries (as mentioned in link below) so wanted to raise it as a possibility.
More info here: https://www.mencap.org.uk/learning-disability-explained/what-learning-disability
If it was me, I would just want to know about as many additional needs/conditions as possible so that I can rule them in as possibilities or rule them out, which is why I am mentioning this.
I know that there are advocacy agencies who can offer support when dealing with professionals. My local authority also has a specific children with disabilities team. If your LA has this they may be able to provide guidance/signposting/advice.