。
She takes great care of her appearance.
Literal
She [topic-は] her own appearance [for/about-に] very-much is-paying-attention.
気を使う (here written 気をつかう, with つかう in kana) means 'to be considerate of, to take care over, to put thought into.' With に, it marks the target of one's careful attention — 'put thought into X.' Distinct from 気にする ('worry about'): 気を使う carries an active, deliberate sense of grooming or maintaining, whereas 気にする suggests passive concern or fretting.