1. This is a special needs child. She will not be able to perform like other students. You should be able to pick what she will play. You can only teach her so much. Understand that. Let her play her 1 note. Don't take it as a discipline problem when she can't do something.
2. It is to your advantage to be seen letting this student play in your band.
3. Check the documentation and see where you can modify. Have this student play what she can. Don't spend a lot of time in class trying to do something. How your other kids will treat this child depends on how you treat her. Can you find a patient student who can work with her individually? You would be surprised what one child can teach another. Also, is there an Aide who accompanies the student to class? You definitely need one.
For the meeting, understand that you are the Professional. Tell that Special Ed teacher what she will or will not be able to do. She will not be an incredible performer, but she will have some success. If the Parents want her to be a star player, they can get her in private lessons - just like every other Parent. Go in with your TEKS, UIL Documentation, lesson plans, etc. You can have this student experience success, in a limited way, in band class. But, you do not have to take her to contest! Make your Administrator understand that you have other students and other responsibilities. You could possibly ask the an Administrator to observe your class. The law says that you must make accommodations for this student, not stop teaching the other kids in the class. If the student becomes a major distraction during class, the Aide can take the student out so she can calm down. Don't let the Special Ed teacher bully you.