Bingo. I think it *might* be her initials.
Or, considering that we know these pictures were taken at or near Disney World, it could be her name. You know how they sell all kinds of things in the gift shops with the kids' names on them... This might say something like "Danielle's Diary" or something similar. It's possible it even says "Disney World". I just think I clearly see a stylized "D" character as the first letter.