Ah okay, that was my second guess but I wasn't exactly sure.
Also besides just being something that would fit with Child Malon, I bet using a bottle would remind people of the "true" way to fight Ganondorf...you can use a bottle to reflect his energy balls, and not have to use the Master Sword. XD
She looks so cute...you know because she's a little kid, pervs. -_-
shes soo cute (not pervy) .and that bottle ...the true hero