。
She's good at sewing.
Literal
She [topic-は] sewing [subject-が] skilled [is-です].
~が上手 ('be good at X') marks the area of skill with が rather than the more intuitive を — a recurring quirk in Japanese where mental and ability predicates take が. The pattern parallels ~が好き ('like'), ~が分かる ('understand'), and ~ができる ('can do'). 裁縫 ('sewing') is a written compound built from 裁つ ('cut [cloth]') + 縫う ('sew'), capturing the two basic operations of needlework — both kanji preserve their concrete verbs even when fused into the noun.