。
She's been down for some reason.
Literal
She [topic-は] [for some reason-なぜか] is-feeling-low.
なぜか ('for some reason, somehow') is built from なぜ ('why') + the question particle か, giving 'why-+-question marker' as a frozen unit — 'reason unclear' / 'somehow.' It's the standard hedge for noting something without explaining it. ふさぐ (塞ぐ) literally means 'to block, plug up,' but in the form ふさいでいる ('is blocking up') it means 'is feeling down, glum, depressed.' The metaphor — that depression blocks or stops up one's spirit — is a quietly evocative example of how Japanese maps emotional states onto physical imagery.