Proxima Bound by Davi Mai

With four hundred years still to travel, we join a plucky teenager, "Thief". She's found a way through the ventilation system, around the radioactive core of the ship and into the front sections. Thief brings back vital components that might help the rear-dwellers connect the ship's computer. For the first time in hundreds of years, there is hope.
But people are disappearing without a trace, and the makeshift hospital is overflowing with cases of a new virus.
It's up to Thief to embark on her toughest mission yet. To crawl through the bowels of the ship, the furthest she's ever been, and find some answers, before there's no-one left alive.
What she finds at the front of the ship, however, is terrifying