In real life, at the time of filming, Jennifer Aniston (Rachel) actually was a smoker but on the verge of quitting.
In his 2019 book Generation Friends, Saul Austerlitz says that despite their usual practice of never admitting when a joke or a script wasn't working, showrunners David Crane and Marta Kauffman thought this episode was so bad, they pleaded with NBC to be allowed to skip that week. However, the network responded that they would take a new episode no matter what shape it was in or how poor its quality was, so "The One Where Rachel Smokes" was aired despite Crane and Kauffman's low opinion of it.
The only time Carol appears in Central Perk.
When Kim (Rachel's boss), asks if she smokes, Rachel says no, because her father would tell her horror stories about smokers. Though in season 2's "The One with the Two Parties", Rachel's dad was shown to be a smoker himself, this is not a plot contradiction; many smokers are eager to dissuade their children and other loved ones from taking up the habit.
At Rachel's party, flowers made out of cups can be seen in vases.