Cancer is just a bad illness. I too have had the experience of trying to interact with family members in the terminal stages. Neither of them were using marijuana, and they were often not coherent (when they were even awake).
Not to diminish your grief, but your aunt might not have been any more available if she had been using other pain management methods. It's just a terrible, overwhelming thing to happen to the body, and it saps a huge amount of the sufferer's energy.
Unfortunately, there has been quite a few deaths in my family in the last decade, and most were on some form of pain management. They weren't always lucid, but none were as perpetually loopy as my aunt was in the last few months of her life. Someone in the forum accused me of being self-centered for simply mentioning this, but her incoherence did add to my, and particularly, my father's (her brother) grief.
Not to diminish your grief, but your aunt might not have been any more available if she had been using other pain management methods. It's just a terrible, overwhelming thing to happen to the body, and it saps a huge amount of the sufferer's energy.