。
She had absolutely nothing to do with the case.
Literal
She [topic-は] that case [from-とは] completely connection [subject-が] not-exist-past.
The と here marks the standard against which a relationship is measured; stacking は onto it gives contrastive emphasis: 'as for that case specifically...' まったく + 関係がなかった forms an absolute past denial. The とは structure carries a slightly heavier, more literary tone than the bare 関係なかった alone — fitting written or formal disclaimers.