Can 3rd degree domestic assult charges be dropped by the plantif before the court date?

Once a victim reports a crime to the police the state takes over and pursues the charges. Your daughter-in-law is not prosecuting the case, so she cannot go the court house and simply have the charges dropped. However, if she expresses her wishes to the prosecutor, the prosecutor should take those wishes into account and could decide to dismiss the case. Whether that happens depends on the facts of the case, the politics at the prosecutor's office and whether the particular prosecutor in question is having a good day. Having a good local attorney for your son can help tip the scales. Keep in mind, even if your daughter-in-law said she doesn't want to be a witness against your son, the prosecutor can compel her to testify at trial through a criminal subpoena.