。
She speaks English well.
Literal
She [topic-は] English [object-を] skillfully speaks.
A flat declarative compliment about her English skill. 上手に modifies the verb adverbially, the standard way to turn a な-adjective into an adverb (な-adjective + に). 上手 itself can be either a noun-like adjective ('skill at') or a praise word, and the boundary between describing someone as 'skilled' and praising them is intentionally fuzzy in Japanese politeness norms — calling someone 上手 at something can come off as warm encouragement as much as a neutral assessment.