、。
At that moment, she was right in the middle of making dinner.
Literal
She [topic-は] at-that-time, dinner [object-を] is-making moment was.
~ているところだった is the past-tense version of ~ているところだ ('in the middle of doing X right now'). The noun ところ ('place, point, moment') captures a specific snapshot in time, and the surrounding ~ている makes it ongoing — 'the in-the-middle-of-making moment'. Sequencing this as past with だった anchors the snapshot to a previously established time. This is the precise way to say 'I was in the middle of X' without the looser implications of plain past progressive 作っていた.