Complex sentence: Her mother, Ellen Cahill Donnelly, was Secretary for Shearson Lehman (later Lehman Brothers) and is the office manager in Brooklyn for the Forest City Ratner Companies, a real estate developer.
Split into simpler sentences: Her mother, Ellen Cahill Donnelly, was Secretary for Shearson Lehman (later Lehman Brothers). She is presently the office manager in Brooklyn for the Forest City Ratner Companies, a real estate developer.