I would think the fact they were kissing would indicate she wasn’t a prostitute.
Never been to a prostitute (I’m a girl) so I wouldn’t know.
But if some guy wanted to pay for a person to sit in his lap in a car and play kissy face...she will get paid for this desire, I suppose.
I just know that, around here, if a couple of kids are caught in a car doing the wild thing they are arrested. It’s been that way for many, many years.