This little girl might be another doll that would have attacked the player in addition to the one that plays the melody. The text "Spooky!! The doll walks by itself!" can be seen at the beginning of the storyline script with the rest of the text from the event. The line that's there in the Japanese version basically says the same thing. As far as I can tell there's no way to activate the text during regular gameplay. If you check the doll before fighting it, the description is just "?" in both versions. Not to mention the doll that's in the game is floating around the room rather than walking. I took a good look at the enemy text in both versions of the game and didn't see anything unfamiliar, so I doubt the battle data for either of these enemies was actually programmed in.
It's also possible that the little girl was going to be an enemy in the ghost house. There's a townsperson in Spookane who says "I don't like the little Rosemary girl!", which again is basically the same in the Japanese version. The Rosemary family you meet in town doesn't have a little girl with them. The use of the name was probably a reference to the movie Rosemary's Baby, which is about a woman who thinks she is pregnant with a demonic child. The original plan for the girl might have been for her to either be another random enemy or the boss and voice that tries to scare the party away as they make their way through the house.
Well, she's now being included in a series of Mother figurines by Banpresto. And guess what.
She was Pippi all along.