That is the same dress she wore at an baseball game last year, I think :P
Sophia Bush has also a dress that looks like Eliza's:
http://i25.tinypic.com/e97qki.jpg
Thank you so much, asho, for the beautiful pictures!
And Thash, mayne she had a small smile at that pic because she had the sun in her eyes or something. It dosen't have to mean that's she's sad :P