Lock and Key (novel)
After her drug and alcohol addicted mother abandons her, child services forces 17-year-old Ruby Cooper to move in with her sister, Cora, who had left for college when Ruby was young. Ruby is upset about this arrangement and continues to wear the key to her old home on a chain around her neck. After learning she will be transferring to a new high school, Ruby attempts to run away but is found out. Nate Cross, Jamie and Cora's next-door neighbor, covers for her. Over the span of the story, Ruby slowly becomes closer to Nate.
Ruby Summers
Ruby has the power to emit force beams from her eyes, like her father, but hers are black and take 93 seconds to regenerate. She also has the ability to transform her body into organic ruby similar to her mother's diamond form. This ruby form halts the aging process and allows her to survive without sustenance, but due to fear that she might "age nearly seventy years in seconds" if she reverts, she has remained in this form for decades.