He had attached a firecracker to her door so that when she opened it, it exploded. She was in such a state of shock at the way her room was decorated that I don't think she even noticed that the firecracker went off until she could smell it!
Her Answer: She went and filled his truck with balloons and put the sign on the dash board. Sticking with the "stars" theme that he used, she attached Star Bursts onto paper stars and outlined the YES with them.
Now all the work begins, finding a dress, finding the shoes, figuring out the hair-do, etc. (All of which I have been told that I am too UNCOOL to be a part of. Gotta love teenagers.)