Set yourself up as an ally rather than an opponent if at all possible. I know that we all want the best for my daughter, Sue, and I can see that you've given her situation a lot of thought. Affirming the good in a situation is one way to gain allies. You are the person who knows your child best, in all situations. The staff knows about pieces of the puzzle and may in fact know the individual pieces better than the parents.
Parents are the generalists.
If you're not an expert on your child, become one. Use the guidelines found in this issue of MonTAGe to assess your child's development and needs. Quote outside authorities as needed. You may need to bring letters, testing results, journal articles, etc. You are responsible for what happens to your child and you have the authority to make the decisions for her.