Fluttershy has always been afraid of the Everfree Forest at the best of times, let alone in the dark of the night; yet this didn't stop her from making her home so close to it in case any nearby animals needed her help. When she hears the sounds of a hurt animal coming from the forest so late at night, her fear again would not stop her from helping the poor thing.

Then the singing starts.

Reading here.
And here.