Actually, I've heard that what's going on there is this-
There's an old lady in one of the buildings off the side of the bridge, and sometimes, she'll tell a story about a very energetic girl who used to play with an Abra before the bridge was built. She'll say this after you see the disappearing girl. Other times, she'll say "Marvelous Bridge is so exciting! I'm taking a rest."
What one YouTube commenter thought of this was - The old lady was the girl who played with the Abra, and she still does, and when she does she turns into the Disappearing Girl.
Just what I've heard...
Look it up on YouTube if you want.