The police video+audio recording of their encounter in the hotel room should clarify whether or not she is really a prostitute. It is legal for the police to record video in a hotel room. Should a cop be able to ruin a woman's life by simply accusing her of prostitution, without recordings or other evidence that support the accusation? Of course not.
If you are asking whether or not I support legalizing prostitution, I suppose that I do.
Welcome to the world as it exists. Usually they just have the word of another cop listening in. These cases generally have one of three results:
After she spends a night in jail, her pimp or madam pays the fine, and they move to another location.
She gives evidence against someone else.
On occasion, the cop is bribed.