。
She wrote a great many poems.
Literal
She [topic-は] a-lot [genitive-の] poems [object-を] wrote.
詩 (shi) covers 'poem, poetry' broadly — including modern free verse and translated foreign poetry. Japanese has separate words for traditional forms: 短歌 (tanka, 31-mora classical form), 俳句 (haiku, 17-mora), 川柳 (senryū, comic haiku), and 漢詩 (kanshi, classical Chinese verse). Saying 詩 without specifying suggests modern Japanese poetry or unspecified poetic form. The plain past 書いた fits the contemplative texture of looking back over a body of work.