Hello,
Having lived with smokers most of my life I know how tough it is for them to quit smoking. I am wondering if your Mom may be feeling depressed, scared or stressed out. I think this is the time your Mom needs your support the most. Letting her know that you are there for her and that she can talk to you instead of lighting up a cigarette when she's feeling down, depressed or stressed out might help. Like Jen said, anti-depressants might also help your Mom.
Be strong for your Mom, she's going to need it.
Praying for you and your Mom,
Theresa