If you don't know you made the mistake why be upset if she points it out? If you did know it was a mistake why not correct it before examination? If you are okay with minor mistakes then why get upset with the teacher?
If I ask for an opinion or someone is teaching me something new I want to know everything that I'm not doing right. I never get upset over anyone's opinion of anything I do in quilting, right, wrong, or stupid as it may be to them.