It doesn't matter if she doesn't have anything there, she's at the age of being aware, she knows about tits, trust me.
She'll get embarrassed and this should distract her for a while.
Another way to deal with this is do something far more annoying to her, listen to some "pinky" music much louder.
I have an elder sister but I know a thing or two of how to deal with sisters, regardless of age, they are always annoying, even when they grow up, or especially then. You just have to make a plan and execute it.
Another option is to take a walk, or tie her to the street light with a rope, amusing as it may be, might get you into trouble but that's also an option
