An SP is sex for money. Up front. You pay her to act like a whore and to accept being twisted, poked and penetrated as hard and as deep as you want. The mutual respect is on the same level you would have with a car salesman, passenger on a bus or any passing superficial aquaintance. The mutual respect is an act of social grace that hangs by the thread that will eventually break. She will eventually ask for more. She'll allude to her clothing, car or shelter needs. Bring gifts. Tips.
A gold digger tries to get more out of the relationship for the purpose of getting more for herself. Get some guy to subsidize her meagre wages so that she can dress, travel and club without paying her way or doing something good in trade. Not to be confused with a nice girl, with a modest job, who wants a nice guy but does not want a trouble making deadbeat.
A girl is a young woman. (not to be confused with child).
A woman is an older girl.