Hi, in my experience, having had 2 children who needed "special consideration" (for want of a better description) at school, you need to get a letter from a hospital consultant before most schools will agree to anything they view as different from the norm. Unfortunately, local government departments, including education, generally don't respond to evidence from GP's as they are seen as too accessible - that is, some of them are viewed as being willing to put anything in a letter to get you out of their surgery! Similarly, as parents we are seen as possibly suspect as some parents do lie in order to get what they want. So, whether you agree with this view or not, the best way to crack school is to have a consultant's letter supporting what your daughter needs. Even if you have this, you need to be vigilant and check that the school isn't saying one thing to you and doing something different with your child. This isn't (usually) malicious on the part of the school. The problem is that with limited resources, a much wider range of pupils in school compared to times gone by, and pressure on all schools to achieve a "good" or "outstanding" evaluation when OFSTED inspect, individual needs can get overlooked. And we all know it doesn't help when your child looks fine from the outside. Having said this, as in all walks of life, you can get head teachers and class teachers who just don't want to know or who actively take a dislike to parents or children. I firmly believe they form a small minority, but this is not much consolation if it's your family involved.
However, for most of us, it is usually possible to get some or most of what our children need by persevering and not taking no for an answer. Keep a copy of all letters to school and make a written record of all conversations. That way, if something is promised and doesn't happen, you know who made the promise and when and can use this evidence to take things further. Mentioning the DDA in letters can have a very positive effect. Most schools do want to do the best for your child and at the very least, they won't want to be caught out in breach of discrimination legislation.
Hope things go well for you.