The Wide-Awake Princess by E. D. Baker

From chapters.ca:
In this new stand- alone fairy tale, Princess Annie is the younger sister to Gwen, the princess destined to be Sleeping Beauty. When Gwennie pricks her finger and the whole castle falls asleep, only Annie is awake, and only Annie- blessed (or cursed?) with being impervious to magic- can venture out beyond the rose- covered hedge for help. She must find Gwen's true love to kiss her awake.