What a wonderful way to kill the creative ways of a fledgeling quilter. I'm sorry your SIL is in such an un-nurturing environment. This is so old school. I hope you can intervene so she won't lose her desire.
I am probably a teacher's worst nightmare. Went to one of my classes once when I was in a totally frazzled way. I only took my notebook because the only thing I was capable of that day was taking notes. The teacher got really angry with me and told me that it was a sewing class. I told her that I paid my fee and if I simply wanted to sit there and take notes that was my business - not hers. I am not disruptive. She finally backed off. Next week, I went back and all the notes had been turned into the project so I could keep going with the class.
I think that a quilting teacher should encourage the student to sew the 1/4" and explain WHY it is important. The student needs to realize that the better the prep work is done, the better the final result will be. However, it should be up to the student whether she wants to take the seam out and start over.