Hi Joshua! Fawn is one of those elusive fairies. She's a lot easier to find at Disneyland than Walt Disney World.
Tinker Bell's Magical Nook in the Magic Kingdom is the place to meet Tinker Bell and one of of her fairy friends, which could include Vidia, Rosetta, Silvermist, Fawn, Iridessa, or Terrence; however, most recently Periwinkle is the fairy you'll meet there. Unfortunately I haven't heard any reports of Fawn appearing there lately, but I have heard that she's occasionally been spotted at the
Epcot International Flower and Garden Festival. If your trip is this spring during the festival, check out Tinker Bell's Butterfly House where you'll find a Fawn topiary.
Checking the Times Guides at the parks and asking Guest Services if Fawn has any appearances scheduled during your visit are your best bets for tracking down this hard-to-catch fairy. I'll throw some pixie dust your way and hope that your daughter will be able to meet her favorite fairy soon!
Come visit us again at the Moms Panel if you have more questions! We're happy to help!