Are you driving or flying to DL? I love surprises and If it were me I would say we are headed to the movie and already have the car packed so she can't see. Then I would start driving to DL or the airport either one and when she figures out you aren't going to a movie by the length of the car ride or the route you can spring it on her then. Tell her she can do the movie when she gets home or if she really wants to still go DTD is an option.
One time for a surprise trip to DL I told the kids we were going to the DR to get shots. They were freaking out crying and stuff. I kinda felt guilty but then we headed out of town and my daughter saw the buildings were gone and we were in the desert and she got suspicious. It took her an hour out of town to figure it out.

She said I was a mean mommy to trick them but I pointed out that a mean mommy wouldn't be taking them to DL at all now would she????