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I am sorry to hear about this situation. IDEA and 504 plans are to help students with special needs succeed at a public school. It deals with things like grading, special accommodations, and such related issues. What IDEA or 504 Plans do not do is provide "extra security" to the student under such a plan against bullying. So if she is being bullied, then she would have the same recourse that any other student would.
Schools can only do so much to stop the students from being bullied. While schools can technically be sued if they have knowledge of danger and fail to take reasonable steps to prevent it and the child gets hurt, it does not sound like the matter is to that point yet.
The most practical thing that she can do is have her guardian/parent file a restraining order on her behalf against the bullies. See HERE. This can be done regardless of them being students in a public school. Then if the bullies breach the restraining order, they may be actually fined, or held in contempt, or even arrested.
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