Complex sentence: From 1997, Lizzie McPhee took over the role, as Wendy was away, she came back for the last set of episodes from 1998 upto the end of the show's run.
Split into simpler sentences: From 1997, Lizzie McPhee took over the role, as Wendy was away. Wendy came back for the last set of episodes from 1998 up to the end of the show's run.