I'll assume we are talking about you running a game for her, not her playing in your normal dnd game (unless you run a game for a group of 10 year olds of course).
The first thing is to figure out what it is she really wants. Does she want to play Dungeons and Dragons or does she want to play make believe? Does she want to play "the game with the dice and the books" or does she want to play "the game with the fairy princess"? I am betting she wants the latter which is great because it makes your job really easy. The trick here is the same as in any other game you run; give the player the illusion of choice and they will be happy. Run the game like a Choose Your Own Adventure Book, describe the scene/situation and give her a few options (if she is really creative give fewer options and let her come up with ideas on her own). Instead of basing challenges on skill checks/clever spell use/combat capability use puzzles and riddles instead, kids love riddles.
If you want keep a copy of her character sheet but don't give one to her. Instead give her "character sheet" that says things like "can cast healing spells", "is good at riding", "is good at swimmng", "is bad at climbing", "is bad at jumping". So she knows exactly what she can and can't do (ride +5 is kinda vague for a kid). Let her roll dice, roll a lot of dice, but do all the math yourself (if you want to do the math at all, if ever there is a time to roll dice for "sound effects" this is it).
Who knows, eventually she may work her way up to playing the "real" thing. We can always use more gamers in the hobby.
every players are needed. 
