This is a great idea. It is a little difficult buying things for people’s established hobbies since they usually have their basic supplies, but there are some consumables that I think would be good in a gift bag:
*Marking pens/pencils
*Double-sided fusible (like Steam-a-Seam and Heat N Bond) - this is used a lot for appliqué, but it has other uses
*Elmer’s WASHABLE School Glue - this is a little jokey, but many quilters use it a lot, just make sure you get the washable glue - if you want another “in joke”, you could also buy her some freezer paper (availale next to the plastic wrap, wax paper, and aluminum foil at the grocery store)
I know you said tools, but I would also consider buying some fat quarters -- these are 1/4 yard squares of fabric and cost about $3 each (varies from region to region, so don’t panic if they’re charging more than that). I think this is a little more fun as a gift than, say, the aforementioned marking pens, and I think the vast majority of quilters would love to get them as a gift. A dozen of these in different fabrics sounds like it would be within your gift budget.
As far as non-consumable tools goes … maybe a specialty ruler? She likely already has a 6”x24” and some square ones. Most shops seem to sell the Creative Grids rulers, and they’re very good (non-slip). Maybe someone in a shop could recommend a popular one (I’ve heard a lot of people mention Stripology, though I don’t have one myself). The rulers run around $30 and up.
If you can, I would really recommend going to a small local quilt/fabric shop and purchasing there. They’ll have overall better quality items than the chain stores and the employees are usually more knowledgable. Olfa and Clover and two good brands that make a lot of tools and that you’ll find many places.
I hope something I’ve said here ends up being helpful!