If your wife's Bernina isn't making a great buttonhole, it may just need a service. Maybe the feed dogs need to come up? Is she putting the thread through the finger on the bobbin case? That's important for making buttonholes that look great on a Bernina.
The lowest end new Bernina that you can get right now is model 335. It runs for about $980 and has a super easy, fabulous buttonhole system.