well for one ? how old is she and how long has she been smoking ??
people who have smoked for awhile will find it very difficult to quit smoking, and smokers usually will not quit because some one tells them to quit, smokers have to really want to quit for themselves, the longer a person smokes the harder it is to quit..
if she hasn't been smoking very long, say less than 6 months, it will be somewhat easier to quit, but as i said the longer a person smokes the harder it is, also it depends upon how much they smoke per day,
i think the best way to talk to a smoker about quiting is to just calmly express your concern , but don't harrass the issue, just let them know you are concerned and that you hope that they quit soon, for their own health benefits.
and do it in love, this is most important.