。
She's wearing pretty clothes.
Literal
She [topic-は] pretty clothes [object-を] is-wearing.
Bare-bones template for describing what someone's wearing. きれい ('pretty, clean, beautiful') is a na-adjective despite its い ending — irregular among adjectives, since most words ending in い are i-adjectives (赤い, 暑い). きれい takes な before a noun: きれいな服, きれいな人, きれいな部屋. Other na-adjectives that fool learners with this trick: 嫌い ('hated'), 有名 (famous, no い ending). 服 ('clothes') is a singular-plural neutral noun — the form doesn't change with quantity.