When my mom was dying, I used to go out at 2 or 3 am- for a long, long walk and crying spell. I made sure I'd get back before she woke up. I didn't want to fall apart in front of her.
She was always a very difficult patient. The doctor prescribed morphine for her pain. She refused to take it because she didn't want to get addicted to it.
If you have someone else at home to look after her, maybe you could take a walk like I did. You can swear, cry, kick cans and then hold up better once you get home.
I still go off walking when my head needs clearing, or even just to consider what options are open to me. Praying for her and you Phil.