I tend to agree that this doesn't sound like very "slave-like" behavior, though it might be an interesting game. Out of respect, I would not call the girl a prostitute but I would like to explain why I don't feel this is very slave-like or even sub-like behavior that she is displaying, because I fear that you are going to end up being taken advantage of by this little game.

Basicly, what you are allowing this girl to do (whatever you may wish to call her) is top from the bottom. By allowing her to do this she is getting what she wants and controlling the situation. And, I see you being not only broke but broken in the end. If it is a little game, that is fine, but I feel it is truly stripping you of control of the situation. Unless, that is, if she hates sex. Then, maybe, you could be gaining some power or leverage but if she is already an eager beaver (pardon the expression) then she is simply using you to get what she wants and that is very unbecoming behavior for a submissive or a slave.