There is, of course, one problem with copying Miss Militia's power while in custody: Her power isn't just the ability to be armed at all times, but also the necessity. The specific weapon may change (usually a small knife while she's with you, because she's trying to appear non-threatening, but her control isn't perfect), but she is never not armed. You don't mind picking up another permanent power, it's just that things are likely to get uncomfortably hectic if you were to suddenly pull a gun right now.
You did memorize a secondary escape route leading from this room, but you'd still like to avoid having to fight Miss Militia if at all possible. So you try your best to direct your hypothetical subconscious influence over the expression of copied powers towards less exciting results. It mostly involves hoping really hard, because you still don't really have any idea what you're doing or how. But if at all possible you'd like a less exact copy this time around, please and thank you.
When you feel her power slip into place you tense up and furiously repeat to yourself don't be armed, don't be armed, I don't want to be armed. It... works. No weapon appears in your hand. Or maybe nothing you did made any difference, you'd never have gotten an exact copy regardless, and you got worked up over nothing at all. You slump forwards and rest your head on the table. You'll figure out what it does later.