No food, no money, no personnel items.
You can send letters, make them upbeat. Pictures are okay, keep them small. She is working at the hardest level she ever has. Let her know you support and love her.
If you can, try to be there for her graduation, (PIR). It will be one of the proudest moments of her, and your families life.
On an odd note, use a black ink pen when writing her. At night, their "ship", (barracks), will be lighted by a red light. Black ink can be seen best when they reread the letters in their bunks.