。
She speaks English really well, doesn't she?
Literal
She [topic-は] English [object-を] skillfully speaks [right?-ね].
上手 ('skilled') here takes its adverbial form 上手に, modifying how she speaks. The な-adjective 上手 forms its adverb with に — the standard rule for な-adjectives, paralleling 静かに ('quietly'), 簡単に ('easily'). The sentence-final ね solicits agreement: the speaker is offering an observation and inviting the listener to confirm or share it — closer to an English tag question than to a confident assertion. ね is one of the workhorses of conversational Japanese and is largely absent from formal writing.