I do not own TFIOS, John Green does.
It was only a few months after Hazel read Augustus' letter that her PET scans showed that Phalanxor had stopped working. The tumors in her chest were growing again, and rapidly. It was as if they were determined to make up for lost time, and in the process were draining the life out of her like a swarm of vicious leeches. It became increasing hard for her to breathe and her pain continued to rise in its ferocity. By December she was at the hospital full-time, constantly hooked up the BiPAP. Her mother finished her schooling and got her degree. Hazel was happy that her mother would have something to do when she was gone. Issac visited as often as he could, maybe three times a week if was possible. To pass the hours she slept or read An Imperial Affliction, again and again.
Finally she died of lack of oxygen; they couldn't keep enough in her collapsed and drowned lungs. Like Augustus she died while unconscious. A week later her mother was offered a job as a Family Crisis Assistant at Children's. She took it. Hazel's name was added onto Patrick's list, right after Michael's and Augustus'. She was buried at Maxwell Cemetery. Van Housten did indeed make the journey to read the Eulogy, an adaptation of what Augustus had written. Lidwij and Bas came as well, thinking that it was right as they had missed Augustus' funeral. His parents came too. Everyone cried, and despite her suspicions her page was majorly abused the "well-wishers", most of whom she hadn't seen in years and would not have remembered had she read or heard their names, or seen their faces.
Issac continued to attend the support group at the Literal Heart of Jesus. Life continued, and so did death. The world continued to turn and the sun continued to shine. It's a vicious world, and Hazel had a unique view of it. Call it a Cancer Perk.