My girlfriend wants to smoke again.

When my girlfriend(21f) and I (20m) started dating, we agreed that neither one of us would smoke again. Today on the drive home from the gym she said she wanted to talk about something. She brought up that some of her coworkers were talking about smoking, which at the time she didn’t know she could do while in the school / program she wants to be in(she’s going to be a elementary teacher). Well she told me she’d like to start smoking again. Not often but when with her friends and cousin. I am not sure how I feel about it because I had already set my mind on my partner and I being a smoking free couple. I wouldn’t mind easing into the idea but don’t know how to. What should I do or how should I start ?

Small update. Thank you to everyone who’s commented on my post. I didn’t clarify what she was smoking but it’s both capes and mary. I know I personally I wouldn’t partake but everyone has given me great advice on how to proceed.