No need for a new machine as she already has a great one! Can't go wrong with a vintage Bernina. Gift certs are nice but it is so much nicer to have something all wrapped under the tree that she can open. Fun for her and fun for you! (I get the most pleasure watching people open gifts)
I love pattern books, especially ones with loads of patterns in them. There are many to choose from. Some of my favorite all purpose pattern books are:
Quilts!, Quilts!! Quilts!!!
http://www.amazon.com/Quilts-Complet...+quilts+quilts
101 Fabulous Rotary cut quilts
http://www.amazon.com/Fabulous-Rotar...ary+cut+quilts
Big book of Scrap quilts or Big book of Scrappy Quilts
http://www.amazon.com/Scrap-Quilts-A...f+scrap+quilts
http://www.amazon.com/Big-Book-Scrap...f+scrap+quilts
A package of rotary cutter blades is always useful and appreciated!
A set of threads from Connecting threads might come in handy (they happen to be on sale right now!)
http://www.connectingthreads.com/thr...Thread--600901
You could get creative and get a card and make your own gift certificate, promising her a trip to a quilt show and something special from one of the vendors. Maybe say $100 vendor of your choice purchase. You can find out if a show is coming near your town by contacting a local guild or you can see if AQS is doing a show nearby
http://www.quiltweek.com/