Worried about my roommate.

So one of my roommates is 86 years old and has lung cancer. She refuses surgery or chemo and is probably too old anyway. She's been saying that she has been coughing more lately and she is fine with it being almost her time to die.
I don't even know why I am posting this really. She has 2 kids who do not want her living with them. They put her in a nursing home for awhile and she was abused and refuses to go back.
She's very mobile and drives, cleans the house, takes the big trash can to the road, does a lot of stuff. She just wants to feel useful- it's important to her.
She's become like a mother to me because all of my own family is already late.
I have had several friends die from lung cancer and they all lived for years after being diagnosed, so I know she can still possibly hang around for several more years.
I guess I am worried about coming home and finding her dead in her room some day, hopefully not for many years. If that happens, who do I call? Ambulance? Police? Her kids obviously. Do people who are dying know when it's time for hospice? She's on Medicare so I am assuming she will want to die at my house, which kinda gives me the heebie jeebies but I want her to be comfortable and in familiar surroundings.
Like I said, she's very healthy other than the cancer and drives and takes care of herself fine and seems many years younger. But I don't know anything about lung cancer so I don't know what's ahead of me and am hoping that I don't find her dead some day in her room.