You want the boring answer or the inconvenient one?
Let's start with the boring one: You don't. You never use them if you want them alive or every time you do, you assume that she'll get cornerfucked until she dies.
The inconvenient one: Spam the "Rally Trumpet" abillity, and hope she doesn't get fucked up. It won't let her attack, it'll slow you down and it's no guaranty but, hey!
Good question: you would think the slope, but I never get much success with straight up prostitution. It's slow, dangerous, messy, pays badly and isn't very fun. the logic would be that you would want to sell your virginity to one guy that gets the "full package" so you can get the biggest benefit from the larger multiplier. However, the sprite work is somewhat confusing and it becomes hard to do the QTE correctly. So you lose a lot of value there.