Nothing much to add to Polarbear's excellent advice above-- but a couple of quick thoughts.
1. THEY had better not be writing any 504. YOU need to be part of this picture, as well-- you know, since you are one of the world's foremost experts on... your child.
2. 504 is about access-- which is, clearly, being denied to your child relative to classmates. This is completely unacceptable.
3. Diagnosis isn't qualification under 504. This is significantly different than IEP/IDEA. Diagnosis also doesn't lead to a particular menu of accommodations for a particular condition. Ergo-- you may not NEED additional documentation. You see a problem, the teacher sees a problem. Do you both see some obvious solutions? It sounds as though you do-- and that may be all that is needed for those accommodations to be put into action. The ADHD is sufficiently impairing that it qualifies her, yes? Particularly now that ADAA says that mitigating measures (medication) aren't to be allowed when considering eligibility.
4. Consider which life activities are "impaired." If there are checkmarks missing-- FILL THEM IN. This stuff really matters later on.
5. Lillie-Felton. Performance isn't the measure of impairment.
