Don't let this incident bother you! You know what you're doing, to be ready to teach kids to quilt tells me that you've been quilting for many years. The quilt police status doesn't belong exclusively to quilters. Some parents will contest everything the teacher ask. I taught sewing for 10 years in 35 different schools, and I volunteered ifor 25 years in a women' association. Stand by what tou say, do it your own way, you are in charge. Pay special attention to that chilld, you are not aware of what was said front of her,she may be worried that you wll reproach her not having the required fabric or have an attitude, Quilting is fun , she must have fun!