No it's not just a girl thing.
I'm not sure there's a secret! If you find one, you'll win the Nobel Peace Prize.
But C. Lee has it right - don't get involved and be the constant referee because they are getting your attention by doing this stuff. The tattle-tale stuff has to be handled by separating both of them and making them both pay for it. I also had the "if you're not on fire or bleeding or seriously injured" then I'd better not be interrupted by it. That was my "I'm on the phone" rule. It's different if a child says "I really don't know how to handle my sister and I'd like some advice" but usually that's not what they're asking.
They can separate themselves and go to their separate areas. If there's imminent danger like someone's on top of the refrigerator or in the street, if there's an apparent broken bone or your best crystal is involved, then you want to be notified. But this penny-ante stuff is insane. You need to let them know that you will not be sidelined by it, and if they want to cry and whine they can do it privately where you can't hear it or see it.
Don't referee. It doesn't matter how it works out or how it stops, as long as it does.
When they can't get a rise out of you, it will stop. You need to be incredibly consistent and understand that it won't be successful the first few times. Keep with it. The trick is not to get angry or to yell yourself because it reinforces them yelling when they are frustrated. Walk away. Teach them to walk away.
A friend of mine has an expression: "You don't have to go to every fight you're invited to." It's a good lesson for kids to learn, and for us to model for them.
Good luck.