。
She played a key role in this project.
Literal
She [topic-は] this project [in-で] important role [object-を] performed.
役割を演じる ('play a role') is a stock collocation — 役割 ('role, function, part') paired with 演じる ('perform, act'). The same construction works literally for theater or figuratively for organizational and historical roles, as here. 企画 ('plan, project') is the noun for a planned undertaking, distinct from プロジェクト (the loanword variant). 重要な ('important') as a na-adjective modifies 役割. The で marks the arena where the role was played. A common framing in news, biographies, or business memoirs.