River-daughter was another name of Goldberry. She was called this by Tom Bombadil, as she was the daughter of the River-woman of the Withywindle. The name appears in the verse:

O slender as a willow-wand!
O clearer than clear water!
O reed by the living pool!
Fair river-daughter!

By the Withywindle was where Bombadil actually met her. In a song he sings to the Hobbits, he says:

...By that pool long ago I found the River-daughter,
fair young Goldberry sitting in the rushes.
Sweet was her singing then, and her heart was beating!...