Complex sentence: She appeared in the world-premiere of Timberlake Wertenbaker's Our Ajax and appeared in the seventh 24 Hour Plays event for The Old Vic, which featured up-and-coming writers, directors, producers and actors.
Split into simpler sentences: She appeared in the world-premiere of Timberlake Wertenbaker's Our Ajax. Fiona was also a participant in the seventh 24 Hour Plays event for The Old Vic, which featured up-and-coming writers, directors, producers and actors.