I have a Brother PQ1500S. It is WONDERFUL!!!! You can get it on Amazon for about $700.
http://www.amazon.com/gp/product/B00...wsusanmalle-20
It doesn't do embroidery or zig-zag stitches. It just does a single line of stitches, which is perfect for piecing and quilting. It's really fast and strong and heavy, which is just what I was looking for. I've only done a thin quilt so far, two layers of cotton fabric with a thin layer of batting in between, but I don't think it will have a problem with thicker quilts. (Of course, they will always be tricky to maneuver.) It does a straight stitch, meaning a single line of stitches, but your wife will be able to sew curves, etc. with it, such as this: