At World of Disney(DTD) they they a whole section with pen's, pencil's, pencil's case's, note books. I think they even have lap top or I -pad skins, which would be fun and functional. Maybe something for her to put up in her room, Like a picture of the family, holding a sign that say's we love you, or miss you, or just something silly, like all wearing funny hat's. Hair things or cute earings.
I would hit up Goofy's Candy shop for some fun treats, On that note you might want to bring along some baggies, to protect everything, also some tissue to keep everything from moving around.
Ohhh one more idea, check out Basin (DTD), they have cute soap's, with Mickey and Minnie in them, I love their lotion.
On the mailing, I think that you can mail from any resort, I mailed a package from the Poly one time. If you have the box and if it fits it ships, you should be fine. Ask at check in they will direct you.
I know she will be super happy to get a Disney care package!!