Apparently kids being scared of non-face characters is pretty common. I like all the ideas of letting her watch videos and things, to get used to the idea of meeting characters. Maybe keep 1 or 2 ressies, and make one a mostly-face character one, like Mary Poppins and Alice, CRT, or Akerhaus (can never spell that right). Another thing that might help is that, if she has a favorite character, help me make a little gift to give them. You're allowed to as long as it's not food, and she'll have a reason to go up to a character and interact. If you're still concerned since she looks nervous, find the character handler and voice your concerns just in case. As everyone said, characters are usually fantastic about approaching shy kids. A lot will get on their knees to make themselves less imposing, or depending on the character even pretend to be afraid of HER to boost her confidence. But if it will make you feel better you can issue a warning to the handler beforehand. If they're not too busy they can also act as an intermediary between your daughter and the character. A handler can help by talking for said character, helping to keep your DD relaxed and bridging that gap between people and huge teddy bears. Most handlers are fantastic, cheery people who try their best to help out kids like your daughter.
Best of luck!
- G