Sindawe,
If the month-o'-no-MySpace doesn't work, you may wish to try what BrokenMa and I had to use on BrokenKid. She'd been getting increasingly more snotty and spoiled, taking everything she had for granted and acting along similar lines to your niece.
We made her write down a list of everything in her life that was a privilege, and everything that was a necessity. Then we made her either explain why things were necessities (to our satisfaction) or move them to the "privilege" list. At the end, only true necessities (food, clothing, shelter, adequate school supplies) were on the "necessities" list. Everything else (right down to "pencils and paper to draw with, outside of school assignments", and "contact with friends") was on the "privileges" list.
Then we held up the "privileges" list, and said, "as of now, all of these are gone. And they won't be coming back until you earn them back."
We assigned a certain number of hours of "community service", by which we meant "helping around the house in ways above and beyond basic contributory chores" to each privilege (according to how big of a privilege it was and how much she had abused it). That way she could choose what privileges she wanted back soonest, but had to work hard to get each one back.
It took her several months to earn them back, and she hated us at the time. But now, 3 years later, she's told us that it's the best thing we could have done, because it taught her to value the things she has, because she knows that she earned them. She's turned into quite a remarkable young lady.
I don't know if it'll work with your niece, but it might be worth a try.
-BP
