You can call the state attorney's office and tell them that you no longer wish to prosecute. They will have you fill out a declination of prosecution. However, this does not mean that they will in fact drop the charges. They can proceed whether you want them to or not and subpoena you to testify at the trial. Whether or not the Defendant has been charged with DV before will weigh heavily on the prosecutor's decision whether or not to drop the case.
If she completes the diversion program and the case is dismissed her criminal record will show that she was arrested and that the case was dismissed. She will attain the same result if you are successful in getting the state to drop the charges without diversion.
If she wants the arrest off her record she can apply to have it expunged as long as she has never been convicted of a crime.
Once these domestic violence cases are in the hands of the state's attorney, prosecutor discretion takes over almost exclusively.
Your family member's attorney should be representing her and her best interests, not you as a former complaining witness against her. Consider this. What's to say in a few more days you might have a change of heart again and wish to make the case against her? It is for this reason - and others - that the matter is now in the hands of the state and the perpetrator's attorney.
Good luck to you.
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I see that your basic question was answered by Ms. Jacobs, but you now feel that you are under some pressure from the family. As Ms. Jacobs clarified, the State has sole discretion now on whether and how to proceed. If they decide to take the case to trial, they can subpoena you and require you to appear. The outcome is not in your hands.
You may contact the prosecutor and make your wishes known. He does not have to agree with what you want. If he feels that you are being further victimized, or, worse, pressured by the defendant or other family members, he may take diversion off the table and push the case harder. Additional charges may be filed against your family member(s) if the prosecutor feels you are being intimidated. It appears that you might not want this to happen and that you would be satisfied with diversion, so you might want to warn your family member (or her attorney, so that her attorney can advise your family member) to stop talking to you about this. It sounds like the situation is not too bad right now for your family member, but it could get worse.
DISCLAIMER I do not practice law in your state. This answer is provided solely for general informational purposes only. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising