Your grandmother is over eighty years old, and you saw her death in your dream: death means leaving you, and now you are studying in Chengdu, while your grandmother is in her hometown, separated from each other, and can't meet each other. In her dream, it becomes where you will go.
"Grandma said she wanted to go to Chengdu, but she didn't make it when she died." This sentence may be what your grandmother told you and your parents before, saying that she wanted to go to Chengdu to see you, but she was old and in poor health and never had a chance. This sentence is actually a reenactment of previous life scenes.
Grandma's left face turned into a cat face. It seems that this is rather confusing. Actually, your explanation is quite right. You said you read the story of the old lady with cat face. Maybe this story left a deep impression on you. What they have in common is that they are all old ladies, so you combine them invisibly.
I can see that your grandmother loves you very much, and you miss her very much. You are afraid that one day she will leave you. I suggest you go back to see grandma more often in winter and summer vacation.
Finally, I wish your grandmother good health and a long life.