这条复合句中
helen's face lit up with excitement【 when news came --------her essay had won the first prize.】
when 引导的是前面主句的状语从句
在这条状语从句中
news came 【that her essay had won the first prize.】
news 作为主语,that 引导的是另一完整句子,作为主补修饰 news ；谓语 came 前置.
独立句子也一样需要that 作为连词引导：The news came -------- Helen's essay had won the first prize.