In most cases, parents should treat information from an aide, related services provider or teacher as confidential. Use it but do not not attribute it to that person.
The issue is not whether or not the aide has a right to communicate with you. The aide is at the bottom of the hierarchy in terms of power. Is it fair to put her in the position of taking sides with you against her employer? Don't be surprised if she is transferred or fired.
The school is reacting to perceived threats from you by pulling their wagons in a circle. They are preparing to defend themselves. This behavior is not unique to schools - it happens in any organization when there is a perceived threat from the outside
As a parent, your goal is to make the school want to help your child and your family. You will not succeed by writing demand letters or waving law at school personnel.
You will be negotiating with the school on his behalf for many years. Your relationship with the school is polarized. You need to work on restructuring your relationship with school personnel.
In our training programs, we tell parents, "Unless you are prepared to remove your child from public school forever, you need to view your relationship with the school as a marriage without the possibility of divorce."
You need to learn to use tactics and strategies - letter-writing, persuasion, and negotiation.
If you have questions about services not provided, write a short letter to request information about the number of sessions provided, dates, minutes. You can also ask to see notes of the sessions. If you find that your child did not receive services that were agreed upon in the IEP, write another letter to the effect that services that were not provided, and request information about when these services will be made-up.
If you use this approach, the aide (or other school employee) will not be blamed and can continue to provide you with invaluable "background" information.