What's ahead?

If she is sleeping 20 hours a day she may be in her last stage with the dementia. A hospice evaluation might be appropriate at this time. If she does go on hospice care, then the goal is to keep her comfortable, pain free, and as able to interact with family as is consistent with that.

As for the spot on her lung, I imagine that what happens next depends somewhat on where she is in the progression of her dementia. If she is close to end of her expected life span, maybe nothing will be/should be done.

Or perhaps further tests will be performed to determine if that mass is cancer and options will be presented based on the findings..

In general, I think it is good advice to "Don't do the test if you won't do the treatment." Before further tests I'd ask, "what if it is cancer? What would the options be then?"

I am sorry your family is facing this. Hugs.

I think that is a question for your doctors. I think you have to be very honest with yourself about where mom is in her dementia and whether any kind of treatment will enhance or detract from the quality of her remaining years.