Princess Liana is, along with Alexa, is one of the two main protagonists of the thirteenth Barbie film, Barbie and the Diamond Castle.
She is a Princess Of Music who lives in a cottage in the woods with her best friend Alexa. They find a magical mirror that houses a muse apprentice, Melody and hopes to help her find the magical instruments hidden inside the titular Diamond Castle and stop the fallen muse Lydia from destroying them.
She also has a necklace with a magical heart-shaped diamond from the Diamond Castle that protects her from Lydia's evil spells and enchantments whenever she plays the flute.
Trivia
Royalty wise, Liana is the second protagonist to not be royalty at birth, preceded by Queen Erica, who is a queen by marriage. Rapunzel doesn't count because she is on aware of her royal heritage.
She is Also one of the few Barbie protagonists who have no known relatives other than her dog.