Ready to scream
I agree with the poster who said it would be wise to wait before responding. I also find it helpful to invite the parent in to discuss the concern. Many times, things seem to come across in an e-mail in a way that is more nasty than originally intended. What specifically was she complaining about? You can remind her that you are an adult and sometimes it isn't safe or practical to look through a child's eyes. You have to use your adult judgement. If I ran my classroom on the whims and desires of the kids, no one would be learning very much. This doesn't mean that you aren't child-centered. You're right--we often must make decisions for the good of the classroom community.