Does anyone recognise this very good novel? cant find a title or author?

[Nicole]

Its about a family who go on a yacht and the daughter "drowns".. the son is found to have cancer and the family struggle to go on. the mother (i think) goes back to where the drowning happened and finds an earring that she is sure belongs to her daughter and tries finding her as she believes she is not dead. the daughter is eventually found and has been living either with or as an artist.. eventually they reunite and the daughter lets the son die as he wants to in the water where she supposedly drowned.. sorry if its not very helpful but i really want to find this book. i thought it was called 'into the blue' but searches dont match. any help would be great