I'm mad at my sister for saying my name in an online game.
Why did that bother you?
She ruined my game experience.
Don't be mad at your sister for such a small thing. You shouldn't let such minor things get to you.
But it's a sign of weakness.  She has to respect me!
I think I understand the situation, that you take your games very seriously, and that you all use code-names when playing.  However, your sister obviously didn't mean any disrespect when she used your name, and I'm sure the other players have already forgotten about it.  Let your sister know that it upset you, but don't hold a grudge over something so minor.