As I pointed out, she was pathologically self-centered before ever liking Gary. Pretty much every interaction she's had with anyone since the beginning of the comic revolves around what she can get out of it or what's happening to her, to the point that she sometimes seems oblivious even to the existence of other people. She sits on Gary's face when she first shows up and then gets infuriated with him for daring to have his face there. Then she hates Gary until she realizes that he can draw and might be useful as an artist for her comic. A naked woman (Didi) comes in and says, "Do with me as you will." She never questions who this is, what she's doing or what she wants. Her only thought is to start examining her to determine how good a model she'd make for her comic so that she, Yuki, can make money.
Those are just her first three scenes in the comic. I could go on and on. Now like I said, she's not the only selfish person in the comic, but she certainly seems the most consistently, even nonsensically, self-centered.
I... can't actually argue with that. Hm.
While I admit that you have a point here, I can't say that I think it makes her particularly unrealistic, however.
Quoth the raven, "Polly wants a cracker."
Pony avatar by the Great and Powerful DirtyTabs. Lotsa hugs!