I'm a professional longarm quilter. I think her cavalier attitude was astonishing.
If I were in your shoes, I would not have accepted the quilts with the poor tension. I would have insisted that she redo the areas that were not good quality stitching and I would have gone over each and every quilt to point out the areas I wanted picked out and re-quilted. And no check would be going to her until the quilts were done in a satisfactory manner.
Most people do good work. Some people do lousy work. There are good hair stylists and bad ones, good mechanics and bad mechanics, good plumbers and bad ones, good babysitters and bad babysitters. This field of quilting for hire is no different.
I'm so sorry that this happened to your quilts, and I am especailly sad that she had FOUR of your quilts instead of just one!