What kind of referral would you get from this manager if you work yourself crazy? What kind of referral would you get if you relax? What kind of pay increase (or additional hours) are you getting for all your work? More than they get for sitting out smoking? Time to do what you were assigned, not pass on messages or reminders, and let manager suffer for her own incompetence. You are saving her neck but getting no reward. Time to pull back. This is a job, not your life's dream job. If and when the manager begins to make changes, you are willing to help and step up. But not until.
She doesn't need to change her very flawed style until this inventory goes very wrong, headquarters or accounting starts complaining about paperwork or the drop in sales (due to the smokers). Pull back and let her learn.
If she says anything about you not passing on messages, "that would go better coming from you. I'm their equal and I don't want them to think I am bossy."
(I know this sounds harsh, but think about it ... you get all the stress, she gets it easy.)