Spoiled step daughter , please help?

Ok, i need some advice. Im at the point now where im never going to buy my stepdaughter anything ever again and never do anything with her. Anytime I buy her gifts like for birthdays, xmas, and so on, she becomes a spoiled brat. She becomes down right mean and rude. No matter what i get her or what i do with her its never good enough, and she lets you know. If i take her anywhere its never good enough, or when i buy her anything its not good enough. The last time for christmas she said, "That's all?" My mom and dad stopped buying her any gifts because she did the same thing to them. Everytime she opens anything, she is just down right rude. The last time for her birthday she was disappointed left everything here at her dad's and didn't want anything to do with it. Every single gift i buy is throwing money down the drain. Im so sick of her attitude. When I was younger you appreciated any gift. Its not only that. Its everything in general. No matter what i do its not good enough, and she makes comments on how its not. Im to the point to where im done doing anything with her and buying her anything. The last time i took her anywhere, every 2 seconds she kept saying "im bored". Im sick of it. What would you do??