LOTR geek out.
I think Goldberry is a tragic undead, a dead wood nymph who was resurrected by her husband because he didn't want to lose her.
Goldberry is Tom Bombadil's wife in the first book of the trilogy. She's portrayed as a young blonde woman who can make it rain torrentially to wash out all the streams and rivers in the forest, who rests with her feet in water filled bowls, etc. Tom Bombadil tells Frodo and co that her "heart was beating" during one of his expository rhymes, so it seems clear enough that she's dead.
When Frodo and co ask her about Tom, she doesn't really have any answer except a creepily basic statement: "Tom Bombadil is Master." And a few examples of his mastery. She clearly doesn't understand him, and her perspective on him suggests that she just sort of woke up next to this distant figure one day and hasn't learned a thing since. She also recognises Frodo as an "elf friend", implying that she values elves as similarly deathless beings, though she seems more powerful than your average elf...
Another question with regards to her essential species or being: At one point Bombadil says "I'm no weather master, and neither is anything that goes on two legs", but his wife makes it rain... So how many legs does she have?
It seems to me that Bombadil lives forever, but he got lonely, so he picked a pretty spirit of his home forest and bewitched her to be his idea of a wife, and she mindlessly fulfills her duties in the forest for all eternity, long after her heart stopped beating, some corner of her conciseness probably shrieking at the interminable cycle and meaningless of her existence. I don't think it's cruel of Tom, I think he's a force of nature and nature can be bleak and cold sometimes.. i think Goldberry's life might be pretty bleak.
Moral of the story: the world is wide, don't spend your whole life in one place.