You could tell them you would like both. A behavior plan does not have any legal "teeth" to it like a 504. If your child has a 504 it would have to follow him/her through the years. It may be the school is not understanding what PANDAS is...it is a health condition. With a behavior plan they should also do a functional behavior assessment, it may be hard to identify function when what is triggering the behaviors is a cold, strep etc. Therefore I would think a 504 is more appropriate because it will allow for accomdations when she is struggling during flairs. I do work for a school district and have a child with PANDAS, feel free to message me if you need other ideas or help. Good Luck!!