You suppose at this point, there’s no harm in trying the direct approach.
“What’s your name?”
The prisoner seems startled, but not so startled as to actually answer.
“None of your damned business.”
“Fine, if that’s how it’s going to be, I’ll call you Nonev.”
They don’t exactly seem shaken.
“Whatever suits you. I’ll be out of here before any of you see my real face.”
You’ve pulled this trick a few times. Feign confidence in your ability to escape, get your interrogator to think you mean it, they’ll try to figure out your nonexistent plan and squander a lot of time.
It’s not going to work on you.
“Why are you even here? What was the thing you wanted?”
Silence. But you’ve seen enough to know what sort you’re dealing with. She’s silent because she thinks she’ll slip up if she talks about it more. She’ll only talk if she thinks you’re on the wrong track entirely.
“For that matter, why were you hiding?”
“So I could sneak up on someone and disguise myself as them,” she shoots back. “Wouldn’t have bothered if I’d known the potion couldn’t hide my tail, though.”
“And just who gave you the potion?”
“A wizard,” she says. “Where else would I get one? The theater?”
“Fine, then. Where did you meet this wizard?”
Silence. So this is a potentially productive question.
Maybe you can get more out of her if you make a good guess about where it happened.
Time to employ those old guild keywords with a knowing wink.
And then change the subject and ask what happened to her tail.