I have been in your wife's place. I love to make quilts, but could not (physically and artistic-wise) quilt one on my home machine. It takes A LOT of arm strength to quilt with a domestic machine (even stitch-in-the-ditch, SID). Even baby quilts. So I sent mine out and waited up to two months to get them quilted and paid $100 for a throw/twin size quilt. So when I found a 9" throat machine for sale with frame (used) for $1500.00, I grabed it. (It is the Pfaff Grand Quilter). It has a shelf that you put pantograms on (paper with a design repeated on it) that you follow with a laser light. After one year, I have found only one pattern that I really like (over-all squiggly line). So every quilt has this same quilting design on it. I really don't like mounting the quilt on the frame with backing, batting and quilt top. But at least I can complete the quilt by myself. So if your wife really likes to make quilt tops, this might be a way to do it. PS: I have also tried the John Flynn method and didn't like it either. I would love to buy a 13-15 inch machine, but can't afford it right now.
So talk to some more long-arm quilters and get estimates. Your wife may find that the queen size quilts are not that necessary and that a throw/twin would be plenty large enough. Good luck. Tell your wife to not give up. This is a wonderful hobby.