The perception filter keeps her from being detected by the Toclafane, but that's far from the only danger Martha has faced in the past eleven months. She's been menaced by stray dogs and feral humans, almost crushed by falling ruins, very nearly been irradiated, bombed, or gotten caught in any number of crossfires.
Then there are the slower, more insidious threats of hunger, thirst, exhaustion. Some days, most days, she's tempted to curl into a ball and let the world wind down.
But every day she pushes herself to her feet, takes one step, and another, and prays it's enough.