I agree with Laurie's idea of giving her an art camp registration--or some other activity, rather than just stuff. By age nine kids can defer their pleasure for a while instead of needing to rip open a package exactly on their birth date.
I would consult with her, even though she wants to be surprised. She should have some choice in whatever activity you give her. The cost may or may not be your idea of "reasonable" though.....
Summer art "camp"--lots of half-day camps around us, probably around you too; all the "make your own pottery places" do them, local parks and recreation departments have them, arts centers, etc.My friend's kid does a mosaic camp half-days one week in summer and loves it. Another goes to a beading camp at a jewelry and bead shop. You'd need to do some looking online to find these -- check with businesses and you might find these kinds of things if your local arts and recreation departments don't have them.
American Girl also used to sponsor some events (craft events, "meet the author" events etc.) -- look on their web site and see if you can register her for some special event there. Check the age range so it's not too young for her, but nine is pretty much a target age for all things AG. How close are you to an actual AG store with activities etc.? Boston? New York?