。
She spent a long time combing her hair.
Literal
She [topic-は] long time hair [to-に] comb [object-を] was-putting-in.
髪にクシを入れる ('to put a comb in one's hair' = 'to comb one's hair') is an idiomatic expression. クシ (櫛, comb) is written in katakana here. ~ていた marks the ongoing, sustained activity. The sentence captures a detailed, intimate domestic moment.