Interrogate her yourself

"So you don't think I'm a worthy king?" You look at your commander and order, "untie her and leave this woman here. I will extract information out of her myself."

The minister, commander and the soldiers leave you alone with the barbarian.

"You're a fool to think you'll get anything out of me. Should have left it to your soldiers," she said as she got up.

"You think you're so tough. Let me make you a proposition, grab the dagger there and attack me. If you manage to wound me and bring me down, I'll let you go free. If however I manage to submit you. You'll cough up everything you know. Deal?"

"Deal!" She said as she quickly grabbed the dagger and attacks you.

You knew Trajan was a great warrior and counting on his skills quickly dodge her attack. You continue dodging her attacks easily as she is wildly swiping her dagger at you. After a few unsuccessful attacks she starts tiring. You counter her attack and grab her hand and twist it to drop the dagger from her hand.

You land a devastating knee in her stomach knocking all the wind out of her and dropping her on to her knees.

She spots the dagger and grabs it and tries to again swing it at you unsuccessfully. After another couple of unsuccessful swings, you land a couple a big punch again knocking the rest of the air out of her lungs. She tries to swing the dagger one last time as you grab her hand and take the dagger out of it.