。
She dreaded having to tell him what had happened.
Literal
She [topic-は] happened things [object-を] him [to-に] had-to-tell thing [object-を] was-fearing.
A dense, multi-layer clause: the noun 事 ('thing, fact') is used twice, each time as the head of a nominalized clause. First: 起こった事 ('the things that happened') — a relative clause modifying 事. Second: 彼に言わなければならない事 ('the fact that she had to tell him') — another relative clause modifying 事, with the embedded modal ~なければならない ('must, have to'). The outermost predicate 恐れていた ('was fearing') takes this whole nested structure as its object. Japanese's ability to chain relative clauses without overt connectors keeps such sentences syntactically clean even when semantically heavy.