Big folds in the backing are not acceptable, and these should be brought to the quilter's attention. Quilting in the sashing could be looked at as a design decision. I prefer to quilt in the sashing unless it is very narrow and the blocks are outlined, in which case it looks okay unquilted. Borders should be evenly quilted all around. I think you should take the quilt back in, explain your concerns, and see what the quilter has to say. I agree that she may have had someone else do the quilting, but she is still the one responsible for the work.
I don't understand why anyone would tell you not to say anything to her. She is in a business, and needs to know when there are problems with that business. Now that other ladies in the guild have seen your quilt, they will be less likely to take their quilts to her - unless they know that she has fixed the problem.