Smaller craft or hobby items are good.
So are personal items (chapstick, hair products, body spray) especially if they are travel size or a little bigger.
Hair things (ponytail holders, bands, ect if she uses - we can never have enough of those!)
Goodies too ( our son loves the chocolate oranges that are only out at Christmas, so we put 1 in his stocking each year)
I also add scratch off lottery tickets (our SIL won $20 last year)
I also did a serch and came up with this:
http://www.suite101.com/content/100-ideas-for-stocking-stuffers-a163465
It has alot of great ideas.
Good Luck and Merry Christmas!