。
When it comes to her command of French, she's second to none.
Literal
She [topic-は] French's wielding-ability [as-for-においては] anyone [for/to-にも] does-not-fall-short.
This is a high-register sentence packing several formal elements. 駆使 ('skillful use, mastery') is a Sino-Japanese noun — literally 'drive and use' — implying not just knowing a language but wielding it deftly. においては is the formal compound particle of topical limitation, 'in the area of, when it comes to' (combining locative に + topical/contrastive は). 誰にも劣らない ('inferior to no one') uses the universal-with-negative pattern: 誰にも + negative verb = 'to no one.' 劣る ('be inferior') in negative gives the boast its shape: she falls short to nobody.