。
She's currently in the hospital.
Literal
She [topic-は] now hospitalization-during is.
入院 ('hospitalization') combines 入る ('enter') + 院 ('institution'), and ~中 (read ちゅう here) attaches to verbal nouns to mean 'in the middle of, during.' The same ~中 turns up in 工事中 ('under construction'), 営業中 ('open for business'), 食事中 ('eating'). Note the kun-on contrast: 中 is read ちゅう in this Sino-Japanese compound, but なか when standing alone as a native word ('inside'). である gives the sentence a formal, written feel, the kind of phrasing you'd see on an official notice or in a status report.