My mother in law is obese and has high cholesterol. She also has arthritis in her knees and the doctor told her that her ligaments and thinning out. The problem is she smokes and she refuses to stop. The doctor told her to lose 50 pounds. If she doesn't stop smoking, how does this affect her?
Tell her it's her choice whether or not she wants to live long enough to see her grandchildren grow-up.
If I were you, I would say that and nothing else. Her toxic habits are entirely her business, not yours. If she wants to get a heart attack and lung cancer, there is nothing you can do. If you push the issue or nag her, you risk alienating her altogether. There is an old saying: "You can lead a horse to water, but you can't make them drink." You cannot make her eat diet food or stop smoking or exercise. The choice has to be hers and no one else's.