Camp, you dont need her permission ! call the principal and tell him your coming to sit in on his class for a while. Thats your kid. he dont have to be there by law and they are being paid by your taxes to teach . Make them do their job.
I did it for Robert. Before I knew he was autistic. He was shutting down at school. wouldnt talk to anyone. Me being there made him more comfortable and I did it a couple times a week for a while. If it was ok with mama then it was ok with him. He started talking.
Back when I was a good mom before they started out numbering me I would just pop in and sit and watch without warning. Sometimes in the middle of the day. They can't tell you no. Plus it gives you the opportunity to talk with the teacher before anyone else gets to her.. No appointment needed.