。
She had been longing for word from him.
Literal
She [topic-は] he [from-からの] word [object-を] was-longing-for.
Two notable points. からの is a compound particle: から (from) + の (genitive/relativizer), letting 'from him' attach as a noun-modifier ('word from him'). 待ちこがれる is itself a compound verb — 待つ ('wait') + 焦がれる ('yearn') — with a strong, slightly literary flavor of pining.