Complex sentence: In 1995, Caroline Gillmer fell ill, during which time Cheryl was written to be central to key storylines at the time, producers felt they had no alternative, but to temporarily recast her with former "Prisoner" actress Colette Mann.
Split into simpler sentences: In 1995, Caroline Gillmer fell ill, during a time Cheryl was written to be a central figure in key storylines. Producers felt they had no alternative, but to temporarily recast her with former "Prisoner" actress Colette Mann.