Other mistake: Aurora is celebrating her sixteenth birthday but there are only 14 candles on her birthday cake.
Continuity mistake: While Maleficent is in her throne room filled with her henchmen in the Forbidden Mountains, she's wearing her large ring on the index finger of her right hand, but in some shots, that ring is either on her left hand or has vanished altogether. (00:16:00)
Continuity mistake: Anytime the eye colors of the fairies are shown, Fauna's are very obviously brown. However, when the fairies are with Aurora after the curse takes place, a close-up of Fauna holding a handkerchief shows her with blue eyes.
Answer: She has shoes. There's no reason given why she's not wearing them. She probably just likes being barefoot when in the woods.
raywest ★