Legal Question in Criminal Law in Massachusetts

The conduct you describe is criminal. The plaintiff in a criminal case is the state so once a complaint has issued only the state can dismiss it. That means the DA makes the decision

There is also an accord and satisfaction, wherein the person who is aggrieved may tell the court that he has been made whole and ask the judge to dismiss the charges. The judge has the discretion to dismiss or to not dismiss. Also, while it is true that the decision to proceed on the case is in the hands of the district attorney's office, they still need your cooperation and testimony to prove its case against your girlfriend, so you do have some say in the matter. The police cannot testify as to what you told them happened, if you do not testify, as this type of testimony from the police would be inadmissible hearsay. Finally, you may have a valid privilege to refuse to testify. Consult with an experienced criminal defense attorney to discuss your options as to how to stop this case from proceeding any further. Good luck.

Consider retaining an attorney to determine whether a complaint actually issued or merely a notice to show cause as to whether a complaint should issue. If it is the latter, you may be able to discuss with the police prosecutor and/or the clerk magistrate your desire that a complaint not issue. Good Luck!