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She sued him over the theft of her money.
Literal
She [topic-は] her own money [subject-が] was-stolen [thing-こと] [over-で] him [object-を] sued.
Passive 盗まれた ('was stolen,' from 盗む 'to steal') sits inside a nominalized clause — こと turns 'the money was stolen' into 'the matter of the money having been stolen.' That noun phrase then takes ~で to mark the cause/grounds of the lawsuit: 'over [the matter of] her money having been stolen.' 訴える ('to sue, accuse, appeal') is the legal verb. The frame [crime のこと]で[person]を訴える is the standard way to specify the basis of a legal action.