I agree, ask her to show you how she can cover the back with 2 yards. It can't be done. I think piecing the back will make it too complicated for the girls. They are just beginners and it is sometimes hard to get the backing to lay flat when it is pieced. Ask the mother how many quilts she has made. I'll bet between the sales girl at JA's and her the number is zero. JMHO
Sue