How can I get my cousin to understand that our parents aren’t going to be around forever?

One are my cousins refuses to except the fact that her dad isn't going to be around forever and he’s getting older. She doesn’t like the fact that her dad isn’t the young man she is use to seeing and she complain to me that his girlfriend had to hit her in the head HARD about the reality of her dad being an old man. She told me she was brutally honest and said it straight to her face that she need to start helping my dad our and LISTEN to him because I only wanna see the past when he was younger. Well I told her that she is right and she needs to wake up and see the reality. Her dad is my dad’s uncle and my grandpa is his brother. My grandpa is 69 about to be 70 so he is five years older than her father. I know it sounds confusing but I’m trying to explain as much as I can. My cousin is autistic and she refuses to see what she see and sometimes we have to be BLUNT with her for her to see the bigger picture. I told her that she needs to start helping out her father and do stuff for stuff I stop depending on her daddy all the time. I even even have talked with her and I’m a year older than her. I get the same thing that my parents are gonna be around forever. It’s heartbreaking but it’s true so how can I get my autistic cousin to understand her point of view?