Put a Collar on her and claim her as your own.

You decide that a girl this pretty doesn't come around all that often even as a **** trader, especially one that is potentially a magic user. You then grab a spare **** collar and leash and put it on her neck and say that she is officially your property, to her shock and horror and the delight of your fellow slavers. "First, let's get you registered as a ****." You then take her to the area in charge of **** registry.

The official there gives you a special orb to be placed into the collar which will automatically copy and store the memories of the **** from the day they were born until now and will also compel the **** to follow orders if they refuse or tricks them into returning if they try to escape. You thank him and lead your new **** out of the registry area, delighted at the many possibilities in store now that you have such a pretty and valuable ****. "Now then, what to do with you first, my new pretty ****?"