。
She has a happy look on her face today.
Literal
She [topic-は] today happy-looking face [object-を] is-doing.
顔をする is a fixed light-verb construction: literally 'to do a face,' meaning 'to wear an expression.' It pairs naturally with adjectives in their attributive form — 悲しい顔をする ('look sad'), 怒った顔をする ('look angry'), 真剣な顔をする ('look serious'). The visual evidential ~そう sits attributively as ~そうな, modifying 顔. Note うれしい conjugates in the irregular そう as うれしそう, the regular pattern (い-stem + そう), unlike いい which becomes 良さそう. Mood-from-the-face is part of how Japanese conversation reads people — facial expressions carry social weight, and dedicated phrasing tracks that.