。
She was tidying up her room.
Literal
She [topic-は] her own room [object-を] was-tidying.
片づける ('to tidy up, clear away, put in order') is the everyday verb for cleaning a space by putting things back where they belong — distinct from 掃除する ('to clean' = sweeping, scrubbing). The past progressive ~ていた frames this as ongoing at some past reference time, useful for setting a scene: she was in the middle of tidying when something else happened. The kana spelling 片づける is the standard mixed form (kanji root + kana ending).