Dealing with an "I don't want to know" parent

I'm so tired.  I am my 89 year old mother's only living relative and the person (the only person) with power of attorney - medical and financial.  Two years ago, my father died.  Last year she was diagnosed with colon cancer.   Although her surgeon felt this was probably not going to kill her, it was a slow growing tumor, she had surgery and wound up with a colostomy bag. Six months ago she fell out of bed and broke her hip.  I live in Arizona, she lives in PA.  I left my own family and went and lived with her for nearly two months. It was a drawn out process and a struggle for both her and me.  She was not lucid a lot of the time for the first month after surgery, and there was tremendous confusion about bills, medical insurance and a dozen other bits and pieces.

Today she called me from the hospital and told me that her gallstones weren't really the problem,  she has pancreatic cancer.  Which she doesn't want to treat, which gives her a life expectancy of maybe 4 months.  I respected that, but I spent the morning crying, raging and coming to terms with this, as well as in overdrive trying to be more practical and organized and figure out how I could go to live with her for this last period of her life; the last bout of cancer was hard for her but it was also a disaster for me.

At lunch I tried to call and get some information or speak to the doctor who diagnosed this, and the nurse told me they only suspect it Might be pancreatic cancer.  I know this is crazy and selfish, but I'm so MAD. I'm just wrung dry.  I mean I'm thrilled that this might just be a gallstone after all, but I'm so FED UP with being left in the dark or treated as if the only impact this has on me is sadness.  My life was a shambles the last time because she wouldn't make choices or give me information, because she acted like my role was no more essential than that of her hairdresser.  I know it's egotistical to be so self concerned, but whether she likes it or not, I'm "the one"., the only one.  All of the responsibility ultimately rests on my shoulders, even though she will give up none of the authority.

It turns out she also doesn't want to have a diagnostic test done, which means she might have a three month life expectancy, she might have a ten year life expectancy.

I know that she is terrified of death and she is especially terrified of pancreatic cancer, one of her best friends died a horrible death from it. I know this drama isn't about me. And I agree, she has the right to turn away and say "I don't want to know, I'll live til I can't."  I'm trying to be sympathetic, I'm trying to be compassionate, I'm trying to direct my anger and frustration anywhere but at her.  Help!!