To all the aunts and uncles: Do you discipline your nieces and nephews, especially when they're out of line? Or do you leave it up to thier parents/legal guardian?

I have three nieces, a 7 yo, 5 yo, and 3 weeks old. The 7 yo is rude and has an attitude for days. Her parents really don't discipline her and when they do it's not consistent or firm. When she comes to my house, I do discipline her; I don't spank but put her in time out and take away privileges. It feels futile considering she gets away with a lot of things at home. I don't have kids of my own yet but I love my niece and don't want to see her like that. How do you discipline your nieces and nephews?