Welcome - and sorry you had to come here. I just had to jump in and tell you that my mother was similar to yours - didn't have much hope, was pessimistic and depressed. Still, I would get very annoyed when people would point out all those cheerful cancer sufferers and keep talking about having a positive attitude, because not everyone can be like that and I don't blame them at all - didn't blame my mother for not being chipper! It's hard to imagine what someone is going through when they get a dire diagnosis like this -- it's pretty normal to be depressed, I'd think! Everyone deals with this differently and that's their right.
Also, my mother was a very logical realist, so she wasn't kidding herself. That's not to say that YOUR mother has no options, and I hope they find some way to kill your mother's cancer for good - but she has every reason to feel angry and discouraged right now. I looked into antidepressants and anti-anxiety meds for my mom, and they helped somewhat, though a little late in the game. Your main objective is to support your mom's wishes and foster a life that's free of pain, both mental and physical, so maybe some antidepressants would help. If she's averse to all the medications, look into some of the natural remedies (listed on this site under Alternative Treatments, I think) - though I don't know if there's any natural mood enhancers out there! Really, though, antidepressants, anti-anxiety and pain relievers are the most important tools to fight against the hopelessness, in my opinion.
I know this must be so tough on you -- I tried to be the optimistic cheerleader for my mom, too, but she was too angry sometimes to appreciate it. I coped then and now by trying to put myself in her shoes, and those are shoes that no one should have to wear. I feel now that she really needed someone to talk to her forthrightly, someone to listen to her fears, and since I was her daughter, she didn't feel like she could burden me with that - even though we were best friends. She had a hospice counselor talk to her at one point and it really lifted her spirits - so that's another avenue you may try. They will send out clergy or social workers, even for the caregivers (and God knows the caregivers need some support, too!) Is there a clergyperson or a nonprofit psychology clinic that would have someone she could talk to?
Sorry I have the tendency to go on and on--- I really feel for you and your situation - you have a lot of responsibility on your shoulders and if your mother decides not to continue with any treatment, you'll inevitably feel guilty, like you should have forced it. So I just want to say that you can't force anyone to be any different and you should never blame yourself. You are doing a wonderful job and you are an amazing daughter, so don't lose sight of that! Your mother loves you unconditionally, no matter how remote she may seem right now, and she appreciates all you're doing.
I wish all the greatest outcomes for you and your mother - please keep us posted!