。
She blamed the damage on John.
Literal
She [topic-は] that damage [object-を] John [genitive-の] fault [target-に] made.
~のせいにする ('blame on X') is built from せい ('fault, cause' — usually negative) plus the X を Y にする pattern ('make X into Y'). The damage is the object, and ジョンのせい ('John's fault') is what it's attributed to. せい contrasts with おかげ ('thanks to,' positive cause) and ため (neutral cause/purpose) — Japanese has separate words for the moral coloring of causation, where English uses 'because of' for everything.