My Sister Who Is Age 56 Was Diagnosed With Stage

My sister who is age 56 was diagnosed with Stage 4 Lung cancer 2 years ago and has been doing chemo for the whole time. In Dec, she was diagnosed with cancer in her spinal fluid and fluid around her brain. She started chemotheraphy twice a week since then for the brain. and was doing both together. She has become very weak and has now decided to stop chemo altogether. In Dec, the Dr told her she had 6 months. Now that she is stopping, is there any way to know how long she may have. She will be receiving palliative care soon. I know it depends on each person, but are there statistics on this. Thank you