If you use one of the electric seam rippers, I'd suggest you lay the backing side down (since the thread is already lose there) and have someone help you carefully pull back the batting/top while you give the thread/backing a "buzz cut". On those spots where she traveled back over the quilting, you may have to do some picking with a traditional seam ripper to get it out.
So sorry this happened to you. As a long armer that has been working less than a year now, I also started with donation quilts, and still get plenty to work on. Most I tried a panto on and that usually worked well. While it sounds like your quilt was great (hope to see pictures), I was given a couple that have been nothing but headaches--one the backing was not square and once squared it was too small; one the whole quilt was not squared and a panto would just not work; one the blocks were so unsquared--and even with lose seams in a couple of places--that I ended up doing custom work and taking wayyyy too much time to complete. That being said, I don't blame you for being upset. As a quilter I would appreciate knowing if someone is unhappy with my quilting and giving me a chance to "do over". If you don't long arm, please know that tension is always a much bigger deal with these machines than our domestic machines. And if your long armer is trying to do this for a business, donation quilts do tend to be given less time, and thread, because its very easy to be inundated with charity quilts when folks find out you will do them. I know one long armer(thank goodness she's very fast and also has a computerized machine) that has done about 60 charity quilts in less than a year--she's realizing that she must cut back as it's taking time away from her paid customers.
having picked out an entire charity quilt that I was unhappy with the results(tension, quilt not square, etc) I will tell you that it took two nights in front of the tv in my easy chair--much shorter time than the piecing although no picnic!