Alice used to be a prostitute because she was out on the street and she needed to survive, or was somebody's Sex Slave. She gets involved with Bob and he marries her, and she never goes back to that life again.
But that one person was Bob (and she may or may not have known that at the time).
Or that person was someone very important or famous, and thus Bob is proud because it means in a way that he got a piece of that person too, retroactively.
But Bob doesn't mind at all. In fact, he encourages it.
But financial difficulties forces Alice to do whatever she has to in order to put food on the table until she and/or Bob can find a real job. Bob encourages this.
Parodied: Alice shows up at Bob's residence in Vapor Wear, smelling of cologne Bob doesn't have. Bob is very happy to see her, and doesn't comment on her state of undress.
Zig Zagged: Some people laud Alice for her sexual prowess, others just shake their heads in disapproval.
Alice and Bob are both virgins.
Neither Alice nor Bob are virgins.
No commentary is made on Alice's sex life or Bob's, as it is not relevant to the plot.
Being a slut is neither seen as good or bad.
The writer thinks (and rightly so) that the My Girl Is Not a Slut trope is unfair and dated, and wants to turn it upside down as an act of rebellion.
Alternatively, the writer wants to point how stupid it is to judge someone by their promiscuity and/or lack there of by having characters do the same thing except instead of disliking sluts, they value them.
Lampshaded: "Wow, Alice! Where did you learn to do all that?"
Invoked: Alice becomes a famous porn star, celebrated for her looks and talent.
Exploited: Bob begins dating a prostitute/porn star, marries her, and encourages her to continue her career because it turns him on.
Defied: Alice is saving herself for marriage, or protecting Virgin Power. Or both.
Discussed: "It's great that Alice enjoys sex, and she really is in control of the situation."
Conversed: "Is she really? Or are her hormones in control of the situation?"
Deconstructed: Alice is promiscuous because she's not happy. And all anyone sees her as is someone who will do anything with anyone, which may or may not be true.
Reconstructed: Alice gives up one-night stands and starts wearing more clothing. People start to take her more seriously, and the sex she does have is even better because there's love and respect (not just lust and gratification) there.