My Mom Is 76 Years Old And Has Been Sick

My mom is 76 years old and has been sick for several months. In December, she went for a CT scan and was found to have cancer in her lung (primary) spread to her pancreas, abdomen and has mets to the brain with 4 tumors. The mass in her lung was inoperatable and if she decided against having any chemo, it would only be palliative. She declined rather quickly, lost over 30 lbs. she is now is a nursing facility, just to keep her comfortable. She is in so much pain and so restless, very uncomfortable. I hate to see her this way, how long can this last? She seems to be getting worse by the day.