When my friend became a citizen, I ordered a U.S. flag to be flown over the Capitol the day of the ceremony. Of course, I could not give her the gift until a few weeks later, when I received the flag (along with a lovely letter), but I gave her a card letting her know something would be coming.
The flags have to be ordered through your senator’s or representative’s office; I’m not sure how the shutdown would impact this, but hopefully things will be resolved by the time of your friend’s special day.