。
She stood entranced by the garden.
Literal
She [topic-は] garden [to-に] enchanted stood.
見とれる means 'to be fascinated / entranced by what one sees' — from 見 (look) + とれる (to be captivated). たっていた (立っていた) is the progressive form of 立つ, capturing her standing still while gazing. The combination suggests she was so struck by the garden's beauty that she froze in place.