Apart from the mumsy Barbara, all the female companions on the show so far have been, to a greater or lesser extent, Peril Monkeys, whose primary function is to be menaced by the monsters. It's true that this does happen to Zoe, too - for example, she spends a couple of episodes of The Invasion drugged and locked in a trunk while the bad guys use her to lure Jamie and the Doctor into a trap. But that's combined with the fact that she's a technical and scientific genius.
In a sense, we've been here before: both Susan and Vicki could be described in this way. But Vicki's skills only rarely saved the day, and Susan might as well not have had any, for all she used them after the first episode. Zoe, on the other hand, does so frequently, making her a competent scientific specialist - a Science Geek, whose player has maxed out on Intelligence and science skills. In DWAITAS, she has to take two levels of 'Experienced' to justify her skills, and, she's obviously had plenty of boosts over the course of her adventures, since she's over-powered even for that.
(In fairness, this is also true of Ben, while Jamie appears to be under-powered, and might justifiably get three extra story points to compensate).
