My daughter is 13 and dyslexic as well. We’ve had a hard time with grammar too. This year I tried Analytical grammar but I decided to start with the junior version for her. I also bought the companion dvd (I was hoping watching a dvd and learning from someone else might help).
We are on unit 7 now and I’m absolutely astounded by how well she is doing. She’s diagraming and not missing a word. It’s incredible.
So all that to say I would highly recommend you give Analytical Grammar a try!