I also heard Tiana is in Princess Fantasy Faire.
Check the schedule--there might be a mini-show with Tiana and a few dancers and a band in New Orleans Square, where she will sing several songs from the film. At the end, if your DD is close to the action, she may be chosen to play some tambourines while Tiana sings. (If she doesn't like that, then keep her back and/or make sure that the dancers do NOT give her a tambourine. Or be prepared to play it for her, as I saw some parental figures do.

)
It's definitely no Showboat Jubilee (a much more elaborate show they ran last fall/early winter), but if your DD loves Tiana, that's a place to SEE her, pretty much guaranteed. I do not think it is any sort of meet and greet, though--in one video I saw, a couple girls ran up to Tiana after the show and got little more than a "hi". I get the feeling Tiana just wasn't allowed to stay and greet.
Though I also read somewhere that there was a rainy day where she came out and instead of doing a show she DID have a meet and greet, so you might get lucky. I would make sure your DD doesn't expect to be able to actually MEET Tiana at the show in New Orleans Square, though, to avoid disappointment. (After all, Tiana is a very busy woman and has to get back to her restaurant!

) Then if you happen to be able to talk to her there then it's a bonus, but not something she thinks will happen.
Good luck!