I do not have a 504, so, do not know the specific language or citations best for that, specific to FAs.
However, can you tell us here, specifically what you want this letter to say or to request, on your behalf? I have background in knowing your situation. Not sure if everyone here does. Are you only needing a letter to justify that you should be at all of your dd's parties, or are there other accommodations needed at this time? You might as well think that through, so you can cover it all at the review and updating to your 504.