However, the grammar nazis on wikipedia say that "the original tense can be used provided that it remains equally valid at the time of the reporting of the statement". If that is true, then the grammar rules allow for your "She has dinner with her sister", and your boss can be happy
Example from
http://www.englisch-hilfen.de/en/grammar/reported.htm:
Reported speech - English Grammar
Statements
1) If the introductory sentence starts in the present (Susan says), there is no backshift of tenses in Reported speech.
Example:
Direct speech: Susan: "I work in an office."
Reported speech: Susan says that she works in an office.
2) If the introductory sentence starts in the past (Susan said), there is often backshift of tenses in Reported speech. (see: Note)
Example:
Susan: "I work in an office."
Susan said that she worked in an office.
He said, she said, this is all hearsay anyway
edit: anyway I guess the point is that you probably need to use "She says [not 'she said'] that she has [not 'had'] dinner with her sister" if you don't want to mangle it and still follow the rules of Reported Speech