Thank you for your question. I look forward to working with you to provide you the information you are seeking for educational purposes only.
First off all, with an IEP it is not a one person decision, the IEP is to be decided by the whole team, so their PhD is not the final word on this, it is supposed to be a team effort with the parents, the child's doctor/therapist, the teachers, IEP coordinator and other members of the school team. So, just because their doctor may be saying she does not need this, if you have one specifying what she needs and you believe the behavior issues are just made up to avoid providing for her needs under the IEP, you are entitled to request a due process hearing where you can present your evidence to the IEP coordination team and a NEUTRAL third party to determine what is best for the child. To request the due process hearing you must provide written notice to the school district AND send a copy to the state department of education branch responsible for special education.
The school is obligated by the Individuals with Disabilities in Education Act to provide the tools and assistance she requires to receive a proper education. They cannot put her in a special needs class if that is not the environment that she needs to get the education. If the therapists determines an aide is sufficient or an aide and tutor and some modified class work or assignments would work in a regular class, they are not legally supposed to put her in a special education class.
IF the IEP team decides contrary to her needs, then you request the due process hearing in writing, which as I said goes before a neutral 3rd party mediator to hear evidence from both sides on the issue to determine what is best for the child. If that does not resolve the issue, then you have a right to appeal the due process determination to the school board and then the state department of education.