I heard some horror stories of guys/clients not having the best hygiene.

If you smell that she isn't fresh AND she declines to shower with you, it's best to cancel the date. Don't go through with it. Ask her what she wants for her 10 min, pay, and politely excuse yourself. Then write a review about it, everywhere where you write reviews.

I wouldn’t. I just wouldn’t book her again. If it’s bad enough, I end the appointment early and take the L. That said, this is highly unlikely if you’re booking a well reviewed lady.

Usually by the time a client realizes a provider isn't fresh, it's already too late since the provider had collected their full payment within a few minutes after the date began.

such a provider getting many clients long term, especiallly if she is stubborn about it or even worse, doing it intenttionally knowing full well that she has your full payment and will cause a scene and shout “rape” if you get to aggressive (extreme scenario)

It’s odd they would decline.  

Be good to have a little more information on the area-areas that failed the freshness test...

we tend to spend freely, and never know our balance.  Better to be a spendthrift in this.

Focus more on my preference for her taking a shower than on informing her that she’s not fresh. The request is valid, but focusing on the why (the real why, at least) could impact the session adversely. As someone with skin allergies, I tend to keep that reason handy when asking someone to take a shower.