Depends...is the woman in this profession by choice, or by coercion?
If it's coercion, than it's slavery which is both illegal under the law and immoral to any true libertarian (who value individual choice and not interfearing with the rights of others.)
Not so in this country, where the XII Amendment to the US Constitution did NOT *outlaw slavery,* but rather established it as a governmental monopoly:
Section 1. Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
Section 2. Congress shall have power to enforce this article by appropriate legislation.