Ruiz secretly calls Bull after Sam's murder, survives the engineering assault under a table, and regains enough strength to help Naomi sedate command.
Forced to replace Sam under a two-hour death threat, Ruiz uses a senior private security channel to tell Bull what happened and ask for extraction. Her call gives the resistance direct knowledge of the murder and the weapon timetable. When fighting reaches engineering, she hides beneath a machining table with her arms around her knees.
Bull's force captures the deck before she must choose between completing the laser and dying. Ruiz emerges gray-faced and trembling, barely able to process Naomi's question about Sam's work. Bull places her under Naomi's authority. Although too numb to object, she recovers enough voice when environmental control becomes the task. Infrastructure is her expertise, and she offers to help raise nitrogen on the command decks until Ashford and the loyalists lose consciousness. Rescue converts her from coerced successor into a key technical ally for taking the bridge without another firefight.
Ruiz is a very thin Belter woman with dry-soil brown skin, nearly black eyes, gray shock-stricken coloring, and trembling hands. She wears engineering work clothes.
Ruiz is the rescued infrastructure expert whose covert warning and environmental knowledge bridge Sam's death and Naomi's plan to neutralize command nonlethally.