Offer Gudrun a deal.

You look around the room. Everyone's watching you expectantly.

"What do you guys think?" you say. "I admit it. I know a couple of naughty little charms and I used them to make Gudrun's clothes fall off. Do you think I'm a coward?"

An awkward silence. You hear one or two sheepish "aye, I suppose so"s.

"Or is it exactly what you'd have done, given the chance? After all, it's not like I started the fight. I only stood up for poor Livia over there."

Considerably more ayes this time. Gudrun folds her arms tighter across her prodigious bosom and glares around the tavern, trying to silence people into submission through sheer **** of will. It would probably work, if the sight of her exposed underwear didn't make her so much less intimidating.

"So we agree it's fair to give everyone a peep at Gudrun's undies, and teach her a little lesson about hassling strangers," you say. "But I'll never let it be said that I'm a coward, or one of those perverted travelling warlocks that goes around turning dresses to smoke and compelling suggestible ladies to throw off their clothes and run down the street in the nude. I've only used my powers for justice, and justice must be proportionate. I'll grant that Gudrun's learnt her lesson, and I'll happily let her go without troubling her any further. One one condition."

"And what's that?" says Gudrun, not liking the direction this is going. A lot of people are glancing in her direction and smirking. She can sense the tide of public opinion turning against her.

"I want you to apologise to Livia."

"A true warrior never apologises! It is she who should apologise to me!"

"Well, I guess I have a few more spells I could try out. I just learnt one that makes the victim flap their arms and cluck like a chicken. Does that sound good to everyone?"

"Wait, wait!" Gudrun's blush flares brighter as she considers this unpleasant outcome. She can tell that quite a few people in the tavern wouldn't complain if you kept going. "I'll apologise. But let me apologise to you, first, for calling you a coward. It's clear to me now that you're a noble and upright soul."

"Well, sure. If you want to."

Gudrun sinks to her knees. "Come over here so I can kiss your hand."

"Uh, okay. Whatever floats your boat."

You step close to Gudrun. The second you come within range her arm whips out, throwing a handful of glittery rainbow dust over you. "Hah! Anti-wizard powder! All your wizard powers are hereby negated, and you are at my mercy! Never face off against a barbarian, trickster! We are prepared for every eventuality!"

"Huh. Where were you hiding that?"

"In my... my panties, of course." Gudrun springs to her feet, still blushing very slightly. "I knew it would come in handy one day, what with all those perverted wizards about. Now restore my clothes, boy. No, wait. I have a better idea. Give me yours."

There's a few cheers from the crowd, who don't really seem to care who wins this fight. You shrug. Since you're not a wizard, but a cursed rogue, the anti-wizard dust has no effect on you at all. And since Gudrun has gone back on her promise you figure you're justified in doing pretty much anything you like to her. Should be fun.