I think it depends if she wants Disney magic or if you would literally be sneaking it into her wedding (which I don't recommend). I think there are a lot of things that make one think of Disney. I had mini glass slippers filled with mints and wrapped in tulle at my wedding. Hidden Mickey's in the wedding cake
. Handin out bags of pixie dust to throw at the bride and groom. They have wedding gowns inspired by Disney Princesses http://www.alfredangelo.com/disney/#218 There are Disney themed wedding invitations out there too. You could play music, they even have albums that are instrumental and really subtle.
My wife and I were engaged in Cinderella's castle. Wanted something Disney at the wedding that was not too overstated. We had our first toast in flutes etched with Cinderalla/Prince Charming (purchased downtown). No one really noticed, and we now have them as a keep sake.
We had a Mickey & Minnie Cake topper. We were engaged at Disneyland & spent many weekends there, so it was special to us. Some people knew what it meant, others just thought we picked a cute cake topper.
Assuming your daughter and her fiance also wants some Disney magic...what about using Disney songs for dancing/cake cutting/grand entrance, etc. type songs...
I'll have to think for specific suggestions, but I'm sure there are some great ones!
You could have hidden Mickey's in the bouquet, or on the cake (as a PP suggested). Cufflinks can be an understated touch. I had a small crystal tattoo on my back. Now, truthfully, no one noticed these things. But that was alright, they made me happy!
You should really go to the Disney Wedding Forum. There are lots of people who are getting married and are trying to incorporate Disney. We were married at Disney but if we were married at home we would have looked at cake toppers/wedding invites/favors etc.
Find some "hidden Mickey" confetti in her wedding color and sprinkle it on the tables around the centerpieces. Give her a Cinderella's slipper charm to attach to her garter.
At our wedding, we named the tables after famous Disney couples (Mickey and Minnie, Donald and Daisy, etc.) instead of using numbers. I also had hidden mickeys on my veil.
My daughter and her fiance asked for a hidden Mickey on their cake. They're only telling people who would appreciate looking for it! They also plan to dance their first dance to "A Whole New World." Have fun planning!
I wanted these at my wedding, but changed my location to the disney dream instead! There are Edible Arrangements (fruits) that offer a mickey theme or you can ask for a traditional fruit basket with a hidden mickey, which is a mickey head made out of pineapple. There website is great and you can see what I mean by the disney arrangements.