The teachers at my LQS are great. I've been taking classes there for a year now. They often tell me not to be SO much of a perfectionist as I rip, re-rip and re-re-rip to get something just so. As they say, you're the only one who will notice it and if you stand 5 feet away, will YOU even notice it?
They teach us technique and alternative ways of doing things. In my last class, the teacher called out to me from her station, "What are you doing?" She came running over and asked why I was butting my strips together to make a long border. She showed me a really easy way to sew the strips on an angle. Of course, the class had a whole lot of laughs over my being "chastised." All in good fun.
Tell your SIL to try some other shops for classes. Classes should be for learning AND fun.