First off, if she's any good with computers, it would mostly depend on what type of browser she uses. If firefox, there are several addons to act as a parental spy thinger. I should be in bed, don't mind my language. But anyone in firefox safe mode can disable things like that. Secondly, if it's IE, you should be able to do so through Control Panel > Internet Options, assuming you're using XP.
Secondly, you could very well report her to a mod for breaking the Gaian TOS, so should you be able to actually prove you're her brother, and she is actually 11. She'd either get banned, if this "slutty" things can be proven, or her account would be temporarily banned until her actual birthday occurs. My brother made an account before the 13 year rule, and after it came out, he wasn't able to log back in on that account until then.
Furthermore, depending on your anti-virus/ firewall program, you can set certain sites as "forbidden."
However, honestly, I'd suggest telling your parents. And they can do whatever they like with that. They'll be able to put up programs and passwords and whatever else you like