I happen to know a great deal about dyslexia. As I stated, I'm wary of labeling. And I have done every single thing you have said is needed.
Maybe you've had a student that was a challenge to work with. That would be more helpful to hear about.
I'm not a piano teacher but rather a student who is a challenge to work with and I also have some knowledge about learning disabilities from my work experience.
Having trouble with reading notation is not necessarily caused by dyslexia, that is what I meant, it could be something else. My own experience is with dyscalculia and reading even easy notation can be exteremely tireing for me. So I accept that I won't be performing with music and my teacher accepts that too. I've learned to understand even complicated notation because I need to do it to learn the pieces and sometimes I may even sight read for my own interest at home, but trying to read more than a short section on a lesson is a waste of time. There are also other things that my teacher does not insist I do, but it took some time for us to realize when it's better not to.
I have been with my teacher for 5 years and while we get along fine, she must have had a hard time understanding my strange issues and behavior and why some things don't work out in a "normal" way. She says I'm stubborn, but that's not a negative stament really. I have the will to remove obstacles and life experience to help me do it, but I just cannot learn the way an average person does. But I do learn when I find the right methods. Does you student have the will to learn to play? If so you could concentrate on what works with her and avoid putting too much pressure on her when things are not working out. If you expect her to go through with exactly the similar steps and methods as others, it may never work out if she is some way cognitively challenged.
With my teacher we know we need to move on when we reach a dead end on something at a lesson because I need to work it out alone at home in peace and quiet. Next week in a lesson I usually can do what we were aiming at. If your student gets irritated or moody when trying to do what you ask, it might not be something she can control if she has cognitive issues. Too much pressure can make my brain fry when forced tasks that are too much for me. Doesn't have to be something difficult per se, but something that tires my brain fast such as playing from a score. I try not to release the pressure by behaving badly with my poor teacher, but I sometimes just need to sit quietly for a moment to cool down and then we get to something else. It can seem like I am very upset, but I am often just recollecting my scrambled brain and thoughts.