、。
She was by far the best singer in the class.
Literal
She [topic-は] class [of-の] within [in-で], by-far singing [subject-が] number-one was-good-at.
Two intensifiers stack on top of the superlative: 断然 ('definitely, by far, no contest') and 一番 ('number one'). Either alone would establish the superlative; together they assert it emphatically — 'unquestionably the best, by a clear margin.' うまい ('skilled at, good at') is a more casual / colloquial alternative to 上手, often heard when the speaker is impressed. 歌がうまい ('good at singing') uses が to mark what's done well, a stative-predicate pattern shared with 好きだ, 上手だ, 苦手だ.