I am sorry this happened with your wall hanging. I am glad to hear that the quilter is coming to address your concerns. What I do find a bit disturbing is your saying, "Regardless, it's the last one she'll ever do for me." If you turn this situation around how would you feel? Example, you make a quilt but one of the blocks does not lay flat so she says "You didn't make this square right so I will not quilt for you anymore."
It was mentioned that there should be some type of certification for longarmers. Then shouldn't there be some type of certification for shop owners and "quilt teachers"?
You can go to a beauty salon and get a bad haircut from a licensed professional. You can go to a doctor and get an incorrect diagnosis.
My point is we are human and we all make mistakes.