I don't have a sister, just sister in laws. None of them sew or quilt. My daughter doesn't either, for which I think I'm thankful. She's not only a perfectionist, but with her there are no grey lines. Everything must be done a certain way and that's it period. I'd hate for her to be my quilt police, it would be a disaster!
The good news for you is that your sister is now interested in quilting. With time, perhaps she will mellow.