Ruby trained alongside Alina and Mal at Poliznaya where she befriended Alina, but Alina soon discovered she only did so to get closer to Mal. She was assigned to the infantry of their regiment.
Shadow and Bone
Ruby is stationed at Kribirsk with Alina and Mal. She continues to flirt with Mal, who appreciates her attention, much to Alina's discomfort. She was presumably on the same sandskiff they were when it was attacked by Volcra, and she survived due to Alina's power as the Sun Summoner.
Ruin and Rising
Following the Darkling's coup, Ruby deserts the First Army to join the Soldat Sol. She trains with the Inferni Stigg, who outmatches her in hand-to-hand combat. During the fight, Stigg lights her braid on fire, and another soldier quickly douses it.
When Alina and her companions leave the White Cathedral, they leave the Soldat Sol behind to guard the Apparat and the Priestguards for three days, which should give them enough time to get away. Ruby asks Alina whether she remembers serving together, and when Alina says she does, Ruby cries and calls her "Sankta."
Upon receiving Alina's call for help, Ruby escapes the White Cathedral with Vladim Ozwal, nine other Soldat Sol, and two Priestguards. They join the final fight on the Shadow Fold between Alina's forces and the Darkling's. She is killed before Alina gains the power of all three of Ilya Morozova's amplifiers and therefore doesn't become a Sun Summoner.
After Alina fakes her death, Genya Safin disguises Ruby's body to resemble Alina's. She is cremated as the Sun Saint on the same pyre as the Darkling. Tolya Yul-Bataar describes this as Ruby's "final act of faith."
Ruby was a pretty young woman with a long blond braid, green eyes, and a wide smile. After she joined the Soldat Sol, she got a black sun tattooed on the right side of her face.
Personality and traits
Ruby was a happy, flirtatious girl, but after her experiences in the First Army and with the Soldat Sol, she became watchful and wary. She was particularly dedicated to the cult of the Sun Summoner.