We did the same thing last year but it was a vacation. 7 of us total 3 adults and 4 kids ranging from 3-14. It was really for the kids but we had 4 destinations. On christmas day (6 months before trip) we gave out "inviations to the Amazing Family Adventure" and their 1st Clue. They guessed the clue (it was California). But they didn't know where they were going in CA or what they would be doing and they had no idea what they would be doing or going for the rest of the trip! For each activity and destination we gave them a clue. Utimately we when to LA (Hollywood, Beverly Hills, Santa Monica) then drove to Vegas, caught a flight to Tampa Florida and then drove to Orlando before heading home. The kids had a ball. Before we left we had gym bags (luggage) each in different colors (so they would immediately know that it was theirs) with there names on them. This was like their backpack. Their bags were packed with their clothes and other things they would need on the trip - sunglasses, gum, bathing suit, etc. All of their stuff was in the color theme of their bag and they even had a $ store pencil case to hold there clues.
The amazing race is really like a scavenger hunt with lots of travel involved. Plan out your route. Maybe go to the places you want to take her on her birthday and have the bartender, waiter or hostess give her her next clue at each location. We gave the clues to one of our hotel front desk clerks early one morning. The kids had to go to the lobby and see the clerk to get there next clue. Maybe have her drink a few shots at this bar. Dance at another etc. Find something at another palace. Try this exotic dish at another. Depends on how wild you want to get. And maybe get a nice hotel room or suite for the end of the night (pitstop for the leg of the race).
Good Luck and have fun!
Certified Wedding Specialist and Party Planner