I would argue that the most important symbol in this novel is that of the white elephants of the title. This is because it seems to sum up so much of the difference between Jig and her partner and the way that she is so desperate to do anything to try and save what seems to be a hopeless relationship. Let us remember that white elephants are refered to firstly when Jig looks at the view of teh white hills and she compares them to white elephants. This triggers a minor squabble between them.
Later on, however, she deliberately contradicts herself, trying to make her thoughts and way of looking at the world the same of her partner's, when she says:
They don't really look like white elephants. I just meant the colouring of their skin through the trees.
White elephants are shown therefore to be a symbol of the irreconcilable differences between Jig and her partner, and also the way in which Jig is willing to think of doing almost anything--even aborting her baby--to save that relationship.