We went through the same thing when our DD was nearly 10yo.... infact it was a shocking time. I put it down the fact that I was pregnant with my second and that she felt threatened... it got worse (lots of shouting and loud droning NOOOO NOOO NOOO dramatics when ever we asked her to do (like hand over her laptop) something that she didn't want to do for about a year). She has an incredibly loud voice (every teacher she has ever had has pointed this out to us, just incase we didn't notice) and we felt that the entire neighbourhood could hear her. I mean, she would sit in her room and moan/drone at the top of her lungs for sometimes up to half an hour. What fun that was.
Unfortunately my DH would crack it... I preferred to ignore her and wait until she had calmed down to even begin to reason with her but DH wanted it sorted immediately. It's very hard when you disagree with your partner on how to discipline your child... we disagree more about that than money!

Anyhow, I've no real advice... things are only just starting to settle down now. About an hour ago my DD got into trouble because my DH checked her internet usage and discovered that she was on her laptop from 1am - 3am this morning. She had to hand over her laptop but for the first time she conceded without theatrics. She's lost it for a week now.

Sorry for hijacking. But it's such a demoralising time and I sympathise!