Complex sentence: Rebick was a Trotskyist activist in the 1970s active with the Revolutionary Marxist Group and its successor the Revolutionary Workers League and was editor of the RWL's newspaper, "Socialist Voice" for several years.
Split into simpler sentences: Rebick was a Trotskyist activist in the 1970s, active with the Revolutionary Marxist Group and its successor the Revolutionary Workers League. She was editor of the RWL's newspaper, "Socialist Voice" for several years.