In Pixar's Cars 3, Cruz Ramirez is the young trainer who eventually races for Rust-eze.
Cruz works at the Rust-eze Racing Center and is assigned to help Lightning McQueen prepare for the modern racing season. She understands data, simulation, and training techniques, but she initially lacks confidence in her own ability to compete on a professional track.
Lightning's training trip with Cruz takes them away from the controlled environment of the center. Their journey includes visits to places connected with Doc Hudson's past, allowing Lightning to learn more about his mentor and reconsider what his own future might be.
Cruz ultimately becomes more than Lightning's trainer. At the Florida 500, she enters the race and proves that her skills belong on the track. Her success gives the film a new lead racer while preserving Lightning's role as a mentor.