Melvin's attorney says in a court filing Wednesday her case is "fundamentally dissimilar" from that involving her sister, Janine.
Authorities say Melvin illegally used her taxpayer-funded staff for campaign purposes while she was a Superior Court justice seeking a spot on the state's highest court. Janine Orie is accused of directing the allegedly illegal political activities of Melvin's staff and that of a third sister, former state Sen. Jane Orie.
Allegheny County prosecutors want Melvin and Janine Orie tried together, saying the cases are based on the same acts.
Jane Orie is in prison for misusing her own staff for political work, but was acquitted of using her staff to aid Melvin's campaigns.