The 3 Rings

I'm a new member and a new fan so I could be totally wrong, but I think that one of the themes of the book is that "no one can see all the possible outcomes or that anyone can profoundly change the future" ,so even though Galadriel can see that the quest was to take his life (and I think she was speaking literally), she could not for see that, Bilbo's and Frodo's pity in letting Gollum live would save Frodo's life literally.