。
She's in a really bad mood right now, you know.
Literal
She [topic-は] now quite mood [subject-が] bad [you-know-よ].
機嫌 ('mood, humor') is the right word when emotional disposition is at stake — distinct from 気分 ('feeling, atmosphere') and 体調 ('physical condition'). 機嫌が悪い ('be in a bad mood') is the standard collocation; its opposite 機嫌がいい likewise standard. かなり ('quite, considerably') intensifies the badness without going to extremes. Sentence-final よ asserts new information the speaker thinks the listener should know — a friendly heads-up. Together it lands as 'just so you know, she's in a real mood.'