Well, you do get a hint back in chapter two that Sarah is very talented engineer and that she is more or less wasted as a pilot... and you get another interesting hint about her during chapter three.
Which does raise some interesting question about Sarah... especially in light of something else we learn during chapter three.
I was pretty amazed about RahRah during the encounter with Walker. I think she's someone whos interests in life do not entirely line up with her talents. Which actually makes her a quite interesting character. I actually hope for her to complete her flight training and become a full pilot. It'd make her one of those outside-the-box specialists, which can be both a burden and a boon at the same time. In a way, Chris is an outside-the-box specialist as well, being a bit too impulsive, acting before thinking in case of emergency. Sometimes that's good, sometimes that's bad. Sarah is completely different at that, in that she looks at her job from an unorthodox angle, bringing in knowledge from entirely different fields. Again, sometimes that's useful, sometimes that's a bad thing.
Imagine the crew encountering an advanced alien spaceship while they're on the Vanguard, and the sensors registering an energy spike in the alien ship. Chris would suspect it's an energy weapon loading, and shoot the vessel into pieces. Sarah might expect some means to establish contact and remain calm (but excited). If the aliens turn out to be hostile, you'd want Chris in control. If the aliens turn out friendly, you'd benefit a lot more from Sarah's open mind.