Your friend should definitely correct her error, since you are paying for her
work. In using a LA or short/mid arm machine, even though the batting
may be pieced, the quilter should pay attention to any folds, however slight,
and smooth the batting as you do each row of stitching. The top, batting, and
backing should be taut, and held that way by your side "clips".

I am pretty new to longarming (6 months)and couldn't imagine letting it walking out the door that way(the fold). I would definetly want to know! (but can't imagine missing it). Even though it was half way up the quilt it would have been removed if I had done it. Yes, it's time consuming but that's just the way it is.
Sorry for your experience.But don't let one person, keep you from all the other more careful longarmers there are, many who are on here who's work looks fabulous.