My 14 Year Old Niece Gets EVERYTHING She Wants?

And i mean EVERYTHING. Last year she got new (expensive) clothes, expensive watch new iPhone7 ect ect. This year she's getting like $1000 worth of new clothes by big brands like calvin Klein, Nike, Adidas and other brands like that, even new shoes that cost like $300, make-up brands like Mac. Everything she asks for she gets. Her mum, had to start working because she doesn't have enough money for her daughters tastes. And she drives her everywhere. My niece does work, but doesn't ever buy her mom a good gift.
I don't know why my sister is doing all of this for her. Like i'd be fine with it, if her daughter was grateful. But if she doesn't get what she wants, she gets moody and gives everyone dirty looks.
As for my nephew, he doesn't get nearly as much spent on him and he NEVER complains. He's grateful for everything he gets.
Do you think this is okay? Am i like the only person who thinks she a little spoiled?

Added (1). okay, so there are a lot of people telling me to mind my own business. Yes i understand that, and i do. But i HATE the way my niece treats my sister she has no respect for her mother at all. It pisses me off. And me and my sister are very close, so it is my business.
and my nephew gets jealous, and you can see that pretty clearly. I never thought id get this much attention on this.
i was just asking if anyone else has someone treated like this as well, i think its unfair

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