There are several playable Princess Heroes that you can unlock in Rayman Legends.
Unlocking the Princess Heroes simply just requires you to collect Teensies hidden throughout the game to unlock their doors, and then complete the level they are located in.
Here is the list of unlockable Princess Heroes, and how many Teensies you need to collect to unlock their doors.
Aurora – 35 Teensies
Barbara – 15 Teensies
Elysia – 60 Teensies
Emma – 230 Teensies
Estelia – 55 Teensies
Olympia – 155 Teensies
Selena – 170 Teensies
Sibylla – 290 Teensies
Twila – 115 Teensies
Ursula – 90 Teensies