Fancy dress ideas for a 12 year old?

you could be some of these:

miss incredible

Lady Penelope

The Wizard of Oz-Dorothy

Star Wars-Padme Amidala

pink lady

Princess Leia

hermione(Harry Potter)

Velma- Scooby Doo

Scooby Doo- Daphne

Arwen- Lord of the Rings

or

Eowyn- lord of the rings.