Question

-----she was invited to the ball made her very happy A.what

Answer 1

主语从句中that只起引导词作用,不做成分也没有意义she was invited to the ball 成分意义均完整.

而what一般在从句中做主要成分（主语,宾语等）,且有意义（可根据句意灵活翻译）,如：

1.That he came late again made the teacher angry.

2.What he said in class made the teacher angry