I feel your pain-I had a similar experience once. My suggestion would be to speak with her about your unhappiness over the poor quality of work and tension problems. Who knows, with good constructive criticism she may challenge herself to gain professional skills and reduce her fee while still learning. Here's opportunity for a win-win, she learns from the experience and you get cash back for a less than perfect quilting job. Having her redo the work may still not get you your desired outcome.
What have others done in the past with a similar situation? I know having plenty of backing, batting, and a good squared up quilt is important for longarm quilters.