It happens to all of them eventually.
Some seem to be born with it, others grow into it. When it will happen is influenced by a variety of factors including but not limited to: older siblings (and their gender), friends or regular playmates, a mom's affinity for frilly, whether or not they watch Disney movies/TV, school, etc. No matter the factors it will happen, you can't stop it.
Your girl will go princess.
Don't worry, your not alone, it happens to everyone.
Now I happen to be mother to a little girl who was born loving all things pink, purple and frilly. However she wasn't really into the idea of princesses until recently. She would happily put on her tutu and than wrestle her brother to the ground. Up until recently the only princess that has been part of her life has been Princess Presto:
Pretty mild as far as princesses go and she promotes spelling! Other than that the only time she sees princesses is on her underwear because it's seriously difficult to find underwear for girls without princesses on them!
However I knew the day was coming and we seem to be on the cusp right now, of full fledged princess obsession. She names anything that has on a pink frilly skirt Princess. When we go to peoples houses and they have girls with princess stuff she is attracted to it like a moth to flame. She has seen Cinderella and The Little Mermaid , but since she still lives to be like her brother once was all she needed. But whenever he is not around, Cinderella is who she wants!
What's that you say?
Your daughter's a tomboy? Lives in a house of boys? Loves cars and trains? Refuses dresses? I've heard it all, I've seen it first hand. There is very little chance that you will skate through life without at least a temporary stop in princessville.
One last bit that I will add as evidence to my belief. One of my very good friends daughter (we'll call her Pea) seemed to be impervious to the call of the princess. Her mom was (kind of still is) a bit of a tomboy. Her favorite color was blue. She loved trains and running. She never wanted to wear dresses. Pea actually said to her mom once, "why would I wear a dress? you can't run in a dress".
Hit fast forward. Pea is now 5 and in preschool. Her best friends in her class, they are girlie girls. All princess, all the time. Pea no longer wears blue. Pea no longer wears pants, she needs dresses everyday.
Proof positive, it may take awhile, but even the tough will fall. The power of the princesses is just too strong.
I think it's the tiaras.
* all images from Google Images