Hi, let me try to explain. If you dif deep into it, it's actually rather trivial. Like any human being, Sarah learns everything by comparison. So getting on the ship opens her up to new experiences and emotions, many things she hasn't experienced before and... she loves it. It's not without the help of Sai'mon, who "made her do things" so to speak, but in general, as the game progresses Sarah realizes that she is quite interested in it, though she can't always admit it, but she can't fool her body. Initially it's rather forced and coercive, but then at the end of chapter 2 and near the beginning of chapter 3, Sarah doesn't mind having fun with the Zerg and comes up with more and more elaborate stuff herself. I'm not even talking about what she's willing to do now, she used to have a hard time drinking the weird liquid from the tentacles, and now she's willing to dive into a sperm tank for the essence. Well, it only gets more interesting as it goes!
