GM5, in your shoes I would talk to the principal and have them get that teacher to follow the behavior plan. It is cruel to punish a child because they have a disability, and it should not be allowed to happen. A threat like that is terrible for a child who is already suffering from anxiety; if it were my anxious kid, I know he would not behave at all while under such a threat, not because he didn't want to, but because he'd be terrified, and feeling worse and worse about himself.
A positive behavior plan can definitely be made part of the IEP, and should in your case; at which point it is legally mandated and the teacher doesn't get to choose whether to follow it. She has to. An IEP is good protection for your child.
I will also add that girls are harder to diagnose correctly than boys. Yours sounds a lot like an 8yo girl in our extended family who is creative, imaginative, social-- and has an Asperger's diagnosis. (She is social, but it costs her a lot of energy and anxiety to be social, and she often does it "incorrectly," usually playing in ways that are not quite usual.)
Not saying yours does or should have an AS diagnosis, just saying you may do better with the school if you use private resources to really pin down a diagnosis accurately. Sometimes support from a private expert makes it possible to educate the school about the child's needs in a way that the family alone cannot do. This is how we have made progress with our DS.
It's wonderful that your kiddo has you as an advocate.
Dee
