How has your DD been in the past with meeting people such as Santa? You may want to see how she reacts to the Easter Bunny too. My DDs both did not like Santa or the EB when they were little but WDW was a whole other story. I have pictures of my DDs at about 16 and 18 months hugging and kissing Mickey and all the other characters. We were standing in line to meet Mickey and I put my oldest DD down when it was our turn just to see what she would do. She ran (as best she could at 16 months) to Mickey with open arms. The crowd of people behind us just thought it was the cutest thing they had ever seen. I kinda have to agree :wub:
Just try some of the less visited characters at first and see how she does. Just FYI some of the best times we have had meeting characters has been in Epcot and DS. The lines are much shorter at these parks then at the MK, at least that has been our experience. Epcot also has the Character Spot (I think that is what it is called) It is to your right just past Spaceship Earth going into Innovations. As you walk into Innovations look to your left and it is right there. You go in and basically get into one line and move from Character to Character. Mickey, Minnie, Goofy, Donald, Pluto and Chip and Dale are the regulars there but we have also met other characters there. If you have a Disney Visa you can also go there at certain times and get a free picture of you with the characters.
Hope this helps. It really depends on the child. My girls are 6 and 8 and have been riding Splash Mountain since they were 3 and are now riding all the rides including RNR and Everest without a problem (well, except for a Yeti fear now and then)
Good Luck and have a great time. The characters are great too. If they see that a child is frightened they just move on, they do not try to make the child like them.