Winter Glass by Lexa Hillyer (Spindle Fire #2)
Aurora, torn from the dream world and Heath, plots to assassinate the faerie queen Malfleur, only to confront temptations she never expected. Isabelle, meanwhile, opens her heart to Prince William as they attempt to unite their kingdoms and wage a winning war against Malfleurs army of Vultures. But when the appearance of an unbreakable glass slipper prompts Isabelle to discover more about her lineage, her true identity begins to take shape and her legacy becomes as clear as ice. Devoted half sisters Isabelle and Aurora will grapple with their understanding of love and loyalty as they face a threat even greater than that of the evil queen–the threat of losing each other forever.