I would be a tourist, or someone knew to the city. I could be kidnapped by someone looking for a new girl, or I could see something, witness a murder, and the only way to silence me is to transform me into a prostitute in a new city, or keep me as their new girl.
The gang one would have me taken as a gang leaders girl, with no means of escape, made to submit to tattoos, piercings, and a new life as his, or her girl.
A third idea has me become the slavegirl of a businessman or busineswoman, part of their secret life.
If any of these appeal to you, or you want to know more, let me know.