help my friend wants to smoke!

She is 1 week and a few days pp. she has gone through nothing but hell for 9 months with family and with the father of her child. So yes, I do understand her will to want to smoke.. she says she only wants one, and when we try to research the effects of it with breastfeeding we don't see anything about smoking one cigarette. I understand where she's coming from but I'm trying to talk her out of it because she's gone over a week with out it!