How to deal with older sister in late third stage COPD with diabetes who is stubborn and has a hair trigger bad temper?

She is on many many medications for asthma, COPD, diabetes, blood pressure, and is very overweight and her mobility is growing more limited, though she lives alone and gets around and does for herself with the help of a housekeeper who comes in once a week or so. She lives in another city. We talk on the phone twice a week as I find it is too much for me to handle her anger every day. I visit once a month. Over time she has become a rager. Asking her to tone it down is more incitement to anger. Most conversations are walking on eggshells, she is not interested in more help at home or assisted living or support groups, but is constantly angry and vents and escalates to rage at any frustration. Being around her is similar to being in a car with a road rager, and she will not accept my asking that she not yell at me about things that are not my fault, for even asking a question about something she is complaining about, trying to understand what is going on. I have anxiety depression and panic attacks and migraines due to stress and though working hard on these things and getting treatment have not found a way to deal with her attacks when trying to set some reasonable boundaries as to the verbal abuse and raging, that doesn't trigger my own issues. I understand she is upset that she is dying, of course. It would be a lot easier to help her and be there for her if she wasn't so angry at me all the time and insisting that nothing helps. I know that there are some practical things that do help but she has fears of spending money to make whats left of her own life more comfortable though she could afford it and is relatively secure. Is it common for people in later stages of COPD to become ragers? I have another older sister who has had the same problems with this sister's rage/anger but she is even further away and does call every day, but she says it is affecting her own health. Has anyone found a way to help the problem if it is caused by the later stage of COPD? I wish she would use her oxygen but she does not. I have suggested she might talk to her doctors about some of these frustrations and lack of interest in anything she used to care about, if she is depressed but that triggers more of a rage. We are not and have never been really close, I am much younger and even with all the above issues in much better health (she would not accept that psychological issues are real ones) but I feel obligation to her and grateful for the ways she helped me in our dysfunctional family situation during my childhood.I would appreciate any suggestions.