x Cameronftw
And for you worrying about your sister, yes you can worry but it's stupid to worry. Let her explore the internet. I remember when I was like 8 and started playing various online games, I was a total n00b and would date anything I met. x_x
I'm 14 now and I realized that no matter what people told me I still was a n00b. Nothing can change that. Let her find out for herself what happens.
And if you really don't want her on the game not a big deal, don't tell her your username and you'll be fine, I mean really just right now there's 39,137 people online. Running into her should be a bit difficult.
You need to think like a responsible adult, or someone who's aware of the risks and consequences of what you're suggesting. Gaia is probably not the only thing this 11 year old is doing online.
There are many risks on the internet
worth worrying about. Risks an 11 year old is not prepared for and should not have to learn from the hard way. Exploring aimlessly without supervision is dangerous, especially when you're too young or naive to spot threats, or know what to do in many situations you may encounter.
There's nothing wrong with supervising internet usage. Ideally parents should be doing this, but any supervision is better than none.