。
She's in a bad mood.
Literal
She [topic-は] mood [subject-が] is-bad.
The bare statement of a familiar mood. 機嫌が悪い is the everyday way to say someone is moody, surly, or in a snit — heard at home, school, or the office. The opposite is 機嫌がいい. The word 機嫌 specifically refers to the mood prevailing at a given moment, distinct from 性格 ('personality,' which is durable) or 気持ち ('feelings,' which can be fleeting and intimate).