If you’re willing to take on this project, this might be more work, but easier in the long run. Since I believe there is a difference in size, I would take the whole comforter apart. Then I would layer and quilt like you normally would. You would have one whole piece of new comforter for binding. However, the first thing I would do is ask the friend to return the comforter. Then go choose backing fabric and high loft batting if that’s what she is wanting. Good luck deciding and making. Let us see when you finish all the before and after shots, if you do go forward with this request.