What Irene says makes Steph relax, not the reassurance that she won't turn her in, but the fact she mentions Earth. It's not a phrase someone born in Baedal is likely to say, which means that a) Irene is probably not militia and b) she might even be in Steph's cohort. That all gets filed away as Steph outwardly reacts to the question by ducking her head and smiling with a hint of embarrassment.

"Have you heard of the Johnny Gossamer books? They're these silly detective novels, I think I read too many of them when I was a kid." It's a pretty good explanation, Steph thinks. Her persona romanticized the idea of sleuthing around and solving mysteries.