Regarding the situation as being 'offensive' or 'immature' - courtesans, the medieval predecessors of whores (and the kinds you could meet in RPGs) could be described more as 'mistresses' (i.e. women rich men 'kept - paid for her lodging, life, servants, clothes etc in exchange for visiting them, not necessarily in exchange for umm... y'know what, but also for simple companionship and advice.
You could take this angle and give the 'courtesan' ranks in Diplomacy and Sense Motive and a commoner/aristocrat class.
Courtesans were the predecessors to whores?
Not the legendary Houri (from which whores get their name) of middle eastern mythology?
They predated the legendary "Whore of Babylon"? (Who incidentally wasn't a whore at all, but the term clearly shows that the "World's oldest Profession" is indeed older than the middle ages.)
Courtesans are around today, alive and well and pretty much unevolved. You'll find their modern day counterparts as hangers on for rock stars, flocking to the big winners at the tables of Vegas or Monte Carlo, and on the elbows of the rich and powerful throughout the world . (Think "Trophy Wife" )
Whores, to use the common term the way it was intended, or "professional women" (with the emphasis on the second word) if you want to be polite, are another thing entirely.
They aren't the stereotype girl in her teens with lots of curves, too much makeup and not enough skirt, nor are they all the hollow faced, sunken eyed drug addicts we hear about. Some are in the trade by choice, while others had the choice made for them by someone else.
Many who "get help" getting off the streets end up going right back to it. In some countries it's legal and nobody is forced. In others girls get sold and kept as property.
Any one image you have of the trade is wrong, because there are so many people in so many circumstances plying it.
So if you want to build such a character in game, you're actually pretty free to make up any back story you like for her. It's as "realistic" as any other can be.
Rich girl kidnapped and sold for political reasons? (She can't go home now because no "common woman" can ever inherit the titles she's supposed to have.) Harem girl who's master was killed? Tough street kid looking for an angle and a way out? Upper class lady slumming, looking for excitement? Perhaps someone under a curse, that she can't refuse when offered money? (Saw that one in the old Thieves World books.) Runaway just trying to survive? Drug addict who can't leave her pimp because he's the only one who knows exactly which cocktail of drugs she needs?
Any and all of these can and do happen in the real world (except for the magical curse one, of course). There are college students studying law or medicine who need to pay for tuition.
The bottom line is that in most countries it's a "profession" with a very short shelf life. People get out, burn out or just plain get killed very fast, very young. They're friend, confidant, psychoanalyst, punching bag and occasionally lover. (That last is often the least important part of their "service" by the way.)
