Vintage sewing books or patterns
I got this in Lincoln, NE at an antique store for $8. I love the illustrations.
These aren't old books, but talk about old fabrics.Antique sewing implements
This is a sad iron, heated on the stove. I'll use it for a bookend. Other ideas include antique buttons, thimbles, needle books. Search on eBay under "vintage sewing lot" and you'll get a lot of hits for buttons, lace, patterns, etc. Wrap it in a basket with neat ribbon and it's an instant hit. 
Gift Certificates at sewing stores (Joann's, Hancock, local quilt stores)
Boring for you, but if you your sewing friend can spend hours in one of these stores, this will go over huge!
Fabric/Projects
If you know what they like to make (baby blankets, apparel, quilts) then you can pick a pattern, fabric, and notions (zippers, thread, and stuff) that they'll need to finish. Also, many quilt stores offer kits to make quilts and blankets.
Time
This is the best gift! Give sewing time-take the kids, preferrably over lunch-so your sewing friend can sew! Tell her she MUST sew during this time and not do laundry or clean bathrooms.
Merry Christmas!
