My kid with serious health issues preferred to avoid mentioning them in her essay, which was about something else entirely (ordinary things in childhood). However she wrote a short but poignant paragraph in the supplementary part were they ask if there is anything else they should know about you. The guidance counselor asked us to write a note explaining some course choices including some online work due to illness and he mentioned her accomplishments in spite of them etc. I think the same kind of thing might work for your daughter.
Make sure to apply for test accommodations early- it can take 6 weeks or so.
Here is a list of test-optional colleges or those that deemphasize testing: http://fairtest.org/university/optional
The list is quite amazing.
Don’t assume the 504 plan will follow her. The standard for accommodations is lower at colleges, and professors have more discretion at some places. She would register with the Office for Disabilities, get letters for each professor, take the letters to the professor herself, and explain. There may or may not even be a list of accommodations on the letter. The letter will not divulge the disabilities and the student has to explain unless some staff member jumps in.
Write a letter for whatever professional(s) you deal with with your daughter and list the accommodations you want, then have the professional sign it. And get tuition refund insurance/
There are so many great colleges out there that would love your daughter. Have you looked at the Colleges that Change Live site?
There are schools that are known for being good with dyslexia and other challenges, but it seems as if your daughter may not need one. Still, Landmark has a wonderful summer college prep program for kids about to enter college.