I have absolutely no experience with this type of cancer, but if it was me I would opt for the surgery, and quickly, at least you would be giving her a chance. If amputation is necessary she might adjust a lot better than you think. I wish you luck.
Sorry to read about this diagnosis. We are dealing with a dog with Lymphoma here but I suggest you check a very active and supportive canine cancer community on Yahoo. They discuss many types of cancer and treatments they have had or not had success with. Great group.