I've been quilting since 1990 and own two Pfaff sewing machines. I would not buy any other brand since mine have stood the test of time. Other than cleaning and oiling I have never had one in the shop for repairs. One of mine is 18 years old, the other 12.
Unique to Pfaff machines is that they have an integrated built in dual feed.
A real plus when it comes to machine quilting and sewing on bindings. (Not all low end Pfaffs have this, ask for it)
Regardless of what brand you choose I can suggest some features that I would not want to be without. A needle threader, needle up-needle down
button, (this setting allows for machine to stop with the needle always down or always up, no hand turning of wheel to always reposition needle to begin again), an adjustable buttonhole stitch for machine applique (also referred to as a blanket stitch), the ability to drop your feed dogs for darning or free motion machine quilting. And last but not least the ability to change your needle position to the left or right of center and still do straight stitching. I would want these basic and helpful features before
a mess of decorative stitches. They are the backbone of quilting.
If a machine does not have a built in walking foot ask the dealer to throw in an attachable one. Not a generic but one that is made for the brand you are buying. Also a darning and open toe foot. Hope this is a help to you. These features may be pricier than you had expected but if your wife gets bit by the quilt bug she will want them. If not, these features will make the resale of her machine much easier without a great loss to your original investment.