Assuming your DM is getting the right level of palliative care which you’re happy with, and, as you say, you’re not concerned about other practical matters, I would suggest you use this time to chat about her life.
With my own DM I fabricated an excuse that my DC were interested in our family tree and that I wasn’t sure about a number of things - where she lived as a child, school life, working life, love life, holidays, favourite memories, what I was like as a baby, and so on, which prompted lovely discussions and re-awakened long forgotten memories for her.
There are still things I wish I’d asked her before it was too late, but the conversations we managed were quite precious to me and she enjoyed ‘providing useful information’ for her GC and walking down her Memory Lane.
I’m so sorry your DM is suffering this life limiting illness and hope you realise that she is not unusual in her denial or being reluctant or perhaps incapable of dealing with acknowledging what is happening to her.
Please look after yourself too during this hugely stressful time
💐