Lisa Frank sticker collections. http://www.amazon.com/LISA-FRANK-Sticker-Book-Stickers/dp...
Another thing my mother used to do was when we got new vinyl for the dinner table, she'd cut the old one in half and wash it in the washing machine, then hang to dry. Once dry, she'd give it to my sister to make her own sticker posters. We once even cut measured and taped one to the bedroom door. Friends and family doodled and stickered her door. Best of all, when she was tired of it, it could be rolled up and put up, or tossed into recycling.
If you don't have vinyl on the table that needs changing, you can goto Jo-Anns or Walmart with a fabric section, and buy it by the yard, then hang it with Command strips on the wall, letting her know this is the ONLY place on the wall stickers are allowed.
Hope she has fun.