I love the Gemstone Trilogy

Especially Ruby Red

The Gemstone Trilogy or Ruby Red Trilogy is a series of three young adult fantasy novels by writer Kerstin Gier, originally published in German between 2009 and 2010. The three books are Ruby Red (Rubinrot), Sapphire Blue (Saphirblau), and Emerald Green (Smaragdgrün).
The books have been translated into over twenty-seven languages and sold internationally. They have also been turned into films starring Maria Ehrich and Jannis Niewöhner in the roles of the main characters.

The series follows the story of 16-year-old Gwyneth/Gwendolyn Shepherd, living in contemporary London who discovers she has inherited the time travel gene that her cousin, Charlotte, was said to have. She and Gideon de Villiers are the final two time travelers, with only ten others who lived in the 500 years before them.

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