Is it possible? I don’t know. It doesn’t work to say, “Oh, whether it was a hoax or not, what matters is that she was real in our hearts, for having touched us with her spirit and bravery.” Nuh-uh. She was real and she touched us, or she was fictional and she fooled us. Any middle ground is a self-deception. Read this MeFi entry for some of the financial perspective on that.
I am not about to launch into a full-blown investigation into each entry and picture that ever got posted on her website, and whether these were faked or doctored. But personally, I can’t find it in me to think that it was fake. There was simply too much investment of heart and soul into that year-long blog for it all to have been an elaborate fictional hoax, and not even the cruelest individual would try to take advantage of other people’s sympathy with such intensely touching material.