How can i convince my mom to get an ecig with no nicotine?

It's up to her: People do not stop habits, good or bad, because other people ask or even insist on it. She has to want to change. I am not a fan of e-cigs as a smoking cessation device, although i understand the "harm reduction" arguments. There are better ways to stop smoking. Leave smoking cessation materials with her, don't nag - tell her you love her and want her to have a long/healthy life.