Incidents are not unique and isolated. Risk management has data about litigation or settlement costs associated with repeat offenders. Treat seriously stress claims and reports of psychological injury. They are as counterproductive as physical injuries and last longer. Stop blaming victims.
Bullying is a safety and health issue.
Do not compel the injured target to participate in a dispute resolution process in which she or he faces directly the perpetrator. Think how unconscionable it would be to ask a battered wife to compromise herself further in negotiations with her abusive spouse. Interest-based conflict resolution models suggest that the needs of each side must be met. The bully has had her way during the years the abusive relationship was allowed to run uninterrupted by management. Purge, don't promote, the bully.