Well, you’re definitely not Nicki.
Of course this is true, but then neither are you, and the fact that my reading of your words is very different from yours shows that you can't conclude that she
for sure wouldn't react negatively to being told such a thing. And that the claim saying things like that is fully reasonable is dubious -- because i don't think i'm the only person in the world who'd interpret them in such manner, and so there's certain likeliness your "fully reasonable" statement could badly backfire.
Pretending that her offering sex and you giving her 20k are unrelated (especially considering there were whole years when she could have fucked you if she wanted to) is silly, and disingenuous. Nicki is smarter than that.
And why exactly does it have to be
pretending? You think that it's not possible for Nicki in the prologue of the game to want fuck Guy without him doing her favors?
Nicki didn't fuck Guy whole years yes, but that was while her own boyfriend didn't show himself to be a dipshit willing to doll her up just so another guy would give her money. It was also whole years during which Guy didn't prove himself to be a friend good enough to help Nicki with serious matter without asking anything of her in return, even though he could ask for a lot. Finally, it's quite reasonable to think that Nicki's feelings towards Guy could evolve and change over those years. Overall, what she did or didn't years back and what she would want to do in the present are far from one and the same.
I think what is silly is boiling this situation to "Guy gave her money" like that's the only factor in this whole situation that could possibly matter and drive Nicki's decisions.