she has super hearing (all blind people who do martial arts do)
and she "sees" via earthbending and since ...so it seems logical that she could since something moving in the air (really fast and thus making noise) if it was a rock or not.
Also earth benders can make rocks float exc so if she really "sees" earth bending she should be able to see that too.
however Aang did beat her in "blind bandit" by simple staying quiet and floating
