But if you want to actually buy something (my dh hates to give gift certificates to me) maybe buy a few other size rulers, some extra same size rotary blades (or even another different size cutter than she already has) and some prepackaged fabrics like fat quarters, jelly rolls, etc. in her favorite colors or the colors in your home.You could buy a few things and then do a gift certificate for the rest. That way she has something to open Christmas day and something to look forward to buying later.
Oh and so nice that you want to do this for her that you are willing to ask for advice from other quilters.