Sorry, if it's not useful, then ignore. Just trying to look at it from another angle, ETA: and meant it in a way that might be helpful.
It does sound to me like you have very negative feelings toward the step-daughter overall. But what do I know?
Perhaps it's just a vent and you really are loving and nice to her and *she* is an ungrateful b*tch. I just think there's two sides to everything.
I still think that who pays for dinner is no biggie. Getting too caught up in those details is usually unproductive and depressing.
Anyway, sorry if it hurt, just ignore.