"Old Hundredth" is a science fiction short story by British writer Brian Aldiss.
She is the ward of, and mentally linked to, her Mentor, a giant and ancient dolphin that lives in an underwater cell.
Dandi is an expert in the musicolumns, insubstantial remains of the psyches of people that react musically when intelligent life is near.
Dandi returns to her home, the crumbling remains of a human settlement, where she encounters a bear, one of few creatures than retain human-like aggressive behaviour.
She is able to choose what music she will play when approached by intelligent beings - it is the Old Hundred; All creatures that on Earth do dwell.