。
She's neatly and tidily dressed.
Literal
She [topic-は] neat-tidy outfit [object-を] is-doing.
こぎれい combines the prefix こ- ('small, slight') with きれい ('clean, pretty, neat') — the prefix doesn't really diminish the meaning here so much as soften it: 'pleasantly tidy' rather than 'beautifully clean.' The same こ- shows up in こぎたない ('a bit dirty'), こずるい ('a bit cunning'), こ憎らしい ('a bit annoying') and similar mild evaluations. 服装をしている ('to be dressed in / to be wearing as an outfit') is the standard expression for describing how someone is dressed overall — distinct from individual wearing-verbs (着る for tops, はく for bottoms, かぶる for hats), since 服装 is the abstract concept of 'dress, attire.'