I can understand feeling hopeless, but set it aside and gear yourself up for the meeting. Don't worry about how you're going to get her to follow a 504. You can't control her actions and will feel more helpless if you make that your focus.

Instead focus on being an effective advocate for your son by preparing for the meeting. Here is a link with some things to consider and I really thought this point was important in your case:

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Make sure that there is a discussion of the student's strengths and abilities.

http://ednews.org/articles/27708/1/...-school-or-district-officials/Page1.html

Wishing you the best!