My mother died of emphysema and COPD a few months ago.
She'd smoked regularly from her mid-20's to her early 50's. She'd quit, taken up exercise, and for 25 years afterwards, had an active, fun, and rewarding life - and out of nowhere, the damage from every cigarette she'd ever smoked came calling.
She went from brisk morning hikes to being house-bound in less than a month. She spent the last year of her life tethered to a breathing machine pumping air into her lungs via a tube to her nose.
When she wasn't sitting on the couch coping with fatigue, she was vigilantly monitoring her vitals, trying to find some balance of blood pressure medications, diuretics, other drugs and eating habits that would stop inflammation from strangling her heart and lungs.
After a certain point, she never got a full night's sleep again, because she could never get comfortable. It started to affect her focus, memory, and critical thinking. We lost the best parts of her six months before she left.
The hardest thing I've ever done is holding it together when she was struggling to breathe for several minutes at a time after getting up from the couch and walking fifteen feet.
--
Mercifully, she only truly suffered for a few months. and when the end came, it was under excellent care. The same can't be said for everyone. I've heard of people lingering for a decade.
I dearly hope you can convince your mother to stop - and I mean right now. Dying from emphysema is utterly miserable - it's being on the edge of suffocation every waking second. I wouldn't wish it on anyone.
--
(Pre-emptive: thanks in advance for your condolences, but it's not necessary - my family and I are at peace and healing. I'm not posting this to get sympathy from strangers, I'm posting it for the OP in the slim hope that it can make a difference. I sincerely hope it does.)