The story takes place in the world of "Walkabout". The premise behind this character is a scavenger of non-descript gender who does steretypically "male" things, like rescuing the "macho soldier in distress", it's only at the end of the book that we see this character is in fact female.
So we need the twist at the end not to be pre-empted too much by the shapeliness of the figure...
...the following are some more concept sketches.
It's clear she needs more belts, webbing, storage packs, and other padding to bulk out her frame and cover up the curves for this to work. On the other hand, she needs to be quick, agile, and combat ready in the story.