If prostitution were legal and she showed up for her "date" and was told she wouldn't be paid and she was forced to have sex, it would still be rape.
Even if she is offered money, should she decide NOT to have sex and it is forced upon her, it is still rape.
She can opt out should she wish according to the law, as she should be able to.
It’s like 2 people come into a lawn and garden center and negotiate a price to fix their mowers. Then two friends show up and demand at gunpoint that the proprietor fix their tractors too.
That’s armed robbery and additionally assault if he was brutalized. Is there any doubt that the proprietor would have fixed all 4 tractors if the price was to his liking? Of course not.
If a prostitute chooses to offer a service like sex for money just like any service provider does they need to be held to the same standards of ordinary business practice.
Yes, it would still in reality be rape. No question. In a legal context however, I believe it would be much easier for the defense to argue that only theft had occurred, since the victim voluntarily reduced the act of sex with her to a service to be purchased. The perpetrators then simply “stole the goods” without payment. Still wrong, still rape, but law and the courts don’t operate on a system of right and wrong. They only concern themselves with the law.