Changes all the time

Riding with my mom in the car, seeing how such a small task tires her out is difficult. She has always been so active, always moving but able to sit down and relax. Now, even when she's sitting, she does not seem to truly relax. She is always anxious and living with the burden of lung cancer. It has invaded everything she does. I see this and hurt. My sisters see or hear it when they talk to her and they hurt. I can't help them. I don't know how. My #3 sister (there are 4 of us) lives on the west coast and her way of dealing is withdrawing from life. She is very dependent upon my mom and this has broken her heart. I don't know how to help her. I will make sure I call more often. I'm a bad big sister, I have not called enough.