Not sure how cereal bars is an issue (as a mother of three sons who seemed to have a hole in their leg).

I think you can over-talk some things, and over-react to some things; and it seems your daughter may be getting too much of both from both of you. Save the heavy talks and the heavy hand for the things that really need it (cereal bars aren't it). Pick your battles and let the rest go. They learn from experience sometimes much better from parental talks and lectures and punishments.

I know it would have driven my sons up the wall if I insisted on discussing every little error in their lives. Let her make her mistakes and discover the consequences on her own. Save the big interventions for the bigger issues. Otherwise, she'll start turning a deaf ear.