you should honor your ex-wife's rules to discipline your daughter and vice versa,
you would hope that your wife honers yours. Now, when my daughter was that
age, she always portrayed herself as the poor victim. She would embellish on
how badly she was punished in school by her teachers and that everything was
completely unfounded and everyone was out to get that poor child. Once, she
had me run up to school - that's how convincing and dramatic she was.
Point is: does the potato chip story come from your daughter alone or did
you ask her mother too of what happened? Your daughter inevitably will
make herself the victim in the hopes to get you in her corner.
My advice would be to sit down with your ex wife and talk about discipline and punishment and you both should stick to a mutually agreed upon concept.