I was thinking that Wendy would have her collar removed by a professional pick-locker in exchange for healing his daughter at night in the Mage quarters while her handler was asleep then made her way out of the city, getting the bow and the backpack on the way (she already had the knife).

Though I would accept a way that fit in with your plot. You're joking though about the one you put up, aren't you? Any PC knight characters would be incapacitated, it sounds a bit out of the blue, why weren't the knights able to stop him (doesn't their powers allow them to sense when a mage is about to release a spell), and you didn't want people to start out as servitor because it would take too long, but if that event happened then they just would have immediately been released and the story would continue.