That depends how much trouble they get into, but yeah, let's go with the pirates angle for now.
I'm thinking of going with some sort of "Armored Transport" for the ship. Maybe about fifty to sixty meters long, well armed with a very tough hull. A good ship for doing business in lawless regions of space.
I figure that while the ship is in port, my captured smuggler and your character are brought out, perhaps to be sold. However they manage to outwit/overpower the pirate(s) who are minding them and steal the ship. The other slave girls would be pets of the ship's crew, and perhaps have learned a few things about running the vessel from their time aboard it.
Actually I'd been thinking that perhaps the ship in question was the Pirate Queen's own ship rather than just part of her flotilla. Having her personal
ship and personal
pets stolen would give her cause to come after the escaped girls with a vengeance. Though I kind of like the idea of having the pirate queen accompanied by her pets in her scenes, and that's kind of hard to do if they've already been stolen. (I've also considered making the pirate queen, her crew, and her pets the focus of a RPG, but I'm not sure that would work quite as well as the RPG focused on the escaped slaves.)