。
She speaks English fluently.
Literal
She [topic-は] English [object-を] smoothly-and can-speak.
すらすら is a 擬態語 (state mimetic) for smooth, unhindered, flowing action — speech that comes out without stumbling, reading that goes without snags, paperwork that gets through without snarls. The adverbial と ('in the manner of') after the mimetic is standard for many such words, marking how the action is performed. 話せる is the simple potential of 話す ('to speak' → 'be able to speak'). Unlike 上手に話す, which praises skill, すらすら specifically captures the smoothness of delivery — a performance quality rather than a competence claim.