This is going to sound maudlin, but here goes. 2 years ago this November, my mother died of throat and lung cancer. She contracted the throat cancer first, the lung came later. It was behind her heart so surgery was out of the question.
We found out she had cancer in August of 1999. The doctors were very positive that even though her cancer was inoperable, she could have chemo and radiation, and that should lengthen her life. I used to live in the states, but I now live in England. All I could think of was when should I go back, etc. At the end of October, I got a phone call from my brother saying that I should come home. Oddly enough, I'd already had a plane ticket and was flying home the next day because I had a feeling that Mom wouldn't be here much longer. 11 days after I got home I watched her die.
I'm not trying to make you sad, but I guess what I am trying to say is that you sound like you're close with your Mom like I was with mine. I think because of that, you may have a "feeling" when you should go to her. I did, and I'm glad I didn't ignore it. I don't know what I'd have done if I had stayed in England. I was a lot further away than 5 hours and I knew. I think you'll know as well. I think your heart tells you when it's time.
I'm sorry if I've made you sadder. There unfortunately are no easy answers, are there? I just hope that you are able to be with her. I'll be thinking of you, and I hope you come thru this ok. If you need to talk, just email me.