。
She spoke in a feeble voice.
Literal
She [topic-は] feeble voice [with-で] spoke.
弱々しい (よわよわしい) is a vivid adjective meaning feeble, frail, or weak-sounding — the repetition of 弱 (using the 々 iteration mark) intensifies the weakness. This kind of reduplicative adjective is a productive pattern in Japanese: 重々しい (grave/ponderous), 初々しい (innocent/unsophisticated), 軽々しい (frivolous). The iteration mark 々 stands in for a repeated kanji and works only inside compounds. 声で uses the instrumental で to describe the manner of speaking.