Formal diagnosis of dyslexia and disorder of written expression could get dd better accommodations, such as a scribe or use of voice recognition software or keyboard with spell-check and use of a reader or screen-reading software on tests and assignments, extended time for writing assignments, decreased volume of written work and reduced copying requirements, and other supports that might make a real difference in her ability to learn and perform at the level she is intellectually capable of without having to use all of her mental energy just to manage the basic processes of reading and writing.
ETA: Sometimes schools and other professionals will present accommodations and rehabilitative therapies as an either/or choice, if they were mutually exclusive. I think that it is important to give kids with disabilities a way to get around them while you continue to work on rehabilitating the underlying issues, and that you don't make them give up the accommodations just because they learn some strategies to help them function better, unless it is clear that the accommodations are really no longer helpful. You wouldn't deny a kid with functionally impaired legs crutches just because the eventual goal was to get them to be able to walk unassisted, and you wouldn't tell them that they couldn't leave the house until they could walk there on their own...and you wouldn't necessarily expect that even after that child learned to walk, that they would be able to successfully compete in a marathon without using some assistive technology, even if they could manage to get around the grocery store all right without it.
