This whole thing smacks of the ridiculous "zero tolerance" policies in schools where kids are *expelled* for having a nail file or an aspirin in school.
Look, she obviously was finished with the candy bar. Unless she vomited in the station, the spirit of the law was *not* being violated. It's not like she was opening up a happy meal on the train. I think she expected a little discretion to be used and was shocked at how blind, context-free and idiotic the law enforcement was.