Michelle, this seems like an age old situation. I too was a volunteer art
parent when my children were in school, they are 21 and 28 now. It is always
a uphill battle to be an "advocate for the arts". I would imagine in
addition to the classroom teacher having a "control" problem, you are
somewhat a threat to her. What if the students like you better than her?
Seems like the best solution would be to have her leave the room when you
are working with the children. After some 20+ years of teaching, I still am
uncomfortable to have other teachers in the room when I'm teaching--unless it
is a planned observa- tion. Just a quirk I have!