HUMILIATION USING EMAIL

My wife work as a quality engineer of thier company. She is tasked to evaluate cartoon supplies delivered by a particular supplier. Suppliers are also given standard qualification of cartoons to be delivered. She found out that the supplier delivered them with poor quality cartoon that do not comply to the standards set by the company and she ordered to issue a quality measure report for the said cartoons. the company owner of the cartoon got mad of this and emailed my wife including all the managers and directors of her company that they utilized the correct paper quality. and at the end of his email he included a statement as quoted "im sorry for not giving you the gift you ask of me last year, we are not allowed to do that". These ending statement was forwarded by one of the managers who received the email to HRD manager of my wife's company and the HRD utilized this message as ground for investigation against my wife.

The ending statement was included in the email so that my wife will appear to the company that she disobeyed company code of ethics which is a ground for termination.

My question are?

What kind of case we should file to the person who had damage my wife's reputation in their company?

My wife's company asked the supplier to issue an affidavit of complaint against her as a form of formal complaint, is it our right to bring our own legal counsel during the case investigation?

Can you please englithen us on how to counter false accusation and made-up stories which are untrue?

My wife never contacted the person nor emailed him to asked of something.