It's a very glittery background, that's for sure. I've noticed that younger kids don't seem to be concerned about the clothes. I remember when I was little and watched Digimon, Angewoman was the best thing ever. Then I found a picture of her recently and she really doesn't wear much. :U I just never really noticed when I was little.
Power Girl might be great eye candy for guys, but she's also a strong, independent, smart, capable woman. There's a lot to admire in her, including her not being ashamed of her body. It's no surprise to me that she'd be a good role model.
Plus her new series is really fun. You should recommend it to your niece if she isn't already reading it.