。
She's the best dancer of all the cheerleaders.
Literal
She [topic-は] cheerleaders [genitive-の] among [in-で] [the most-最も] skillfully dance [thing-こと] can-do.
最も~ことができる stacks two formal-leaning patterns: 最も ('most,' formal counterpart of 一番) and ~ことができる (the formal/explicit potential, vs the bare potential form 踊れる). Together the sentence reads as deliberately formal and almost report-like. の中で marks the comparison frame ('among the cheerleaders'). チアガール is a 和製英語 (Japanese-coined English) term — the more standard English would be 'cheerleader,' but Japanese fixed onto the チア- prefix plus ガール. The whole sentence has a stiff, slightly translated feel.