。
She should have been more careful.
Literal
[topic-は] more pay-attention should-have-だった.
~べきだった is the past obligation construction — 'should have done X.' べきだ alone is 'should do' (present obligation); shifting だ to its past form だった shifts the temporal frame to a counterfactual past judgment. This pattern often carries a tone of regret or criticism — the action was needed but didn't happen. 注意する ('to be careful, pay attention') is one of the most common Sino-Japanese する-verbs.