If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Why is she the princess of the ponies? Because of her wild mane, of course!
Click a hairstyle. Click locks of hair, then the color you want them to be.
Click an eye type. Click the girl's iris, then the color you want her eyes to be.
Click the other categories to select a mouth, skin color, and a dress.
Your selections will be rated on the Cool Meter on the right.
When you're done, click Done.
Then click the pony to change its color.