So are we all in agreement that input from the student is fine? And if so then really it is just about how much editing the teacher in the OP intends to do.
The issue is that we are all attributing different intentions to the teacher. My thought when I read the OP was that he was going to edit the letter and add his own thoughts. Her letter was to get a read on what strengths she would like to highlight – things he may just not know about her. Just like a brag sheet.