Well, I guess I can throw out my ideas. What a strange story, though.

Little girls are like the pinnacle of innocence to a lot of people. If you were seeing the story revolve around her, she could be representing your own innocence. Such as, your wish to be protected by something like a father protects a little girl. Also, bathtubs are not only related to little kids taking baths, but a very "vulnerable" spot to be in, emphasizing a hidden fear.

I think the fact that the father read a story about the rubber ducky was emphasizing how it was evil. Such as, it was something that seemed innocent and was even written to be innocent, but in truth it was something that was far from it. The father supposedly knew about rubber duckys and would laugh at the idea that they would be evil. Could the ducky have been representing something that was "cute and innocent" but in reality would take advantage of this disguise to get close to and hurt people or yourself? Or even your feelings of innocence?

Since this was at the end of high school, could it represent fears of the future on your own?