。
She didn't tell me about the accident.
Literal
She [topic-は] that accident [genitive-の] thing [contrast-は] me [recipient-に] not-tell-was.
Two は particles in this sentence — 彼女は marks the topic, and 事故のことは marks contrastive topic. The double-は with one carrying contrast is common when staging 'as for X — and as for Y, this thing didn't happen.' ~のこと wraps 事故 as a discussion topic. The に marks the recipient. The unstated implication: she may have told someone else, just not the speaker — that's exactly the kind of nuance contrastive は is designed to convey.