DLC Nuka-World for Fallout 4 is already available worldwide and one of the main reasons to buy this add-on is the amazing Yader-Girl Rocket suit. You don't need to complete any quests, tasks or goals to get it. In this guide, you will find out the exact location of the Nuka-Girl costume.
Location: Nuka-Galaxy, Galactic Park, at the end of the trip.
Go to the Nuka-Galaxy in the Galactic Zone. After fighting with several robots, you can get the Rocket suit.