I have seen some really good books at babies r us about becoming a big brother/sister. They completely go over from bringing new baby home, daily/nightly life with new baby, the role of being a big brother/sister, and helping mom and dad with new baby. I have gone through the book and think it is amazing at how they describe everything for the older child. I actually got the one for a big brother for a friends son at a shower i did for her and picked out thing from the book (bottles, bath stuff, rattles, etc...) and did a gift basket for the big brother to be. It was just for him to use when his little sister arrives next month to help mom and dad with her. I told him that those were his goodies to help welcome his little sister to the world. Granted he is 8, but that way he can start preparring for the new role he will soon have.
They also have some kid like scrap books for kids to do different activities on welcoming their sibling.
I have also seen a little soft play cube where you can put personal family pictures in the cube. I think it makes different sounds like crinkly noise, rattles, and squeaks. You can personalize the pictures and maybe she could pick out picture of her and to make some personal for her new sibling with just pictures of her in it.