Learn Polish: Powinnam była zareagować szybciej i cię uprzedzić. - I should have reacted faster and warned you. female

Adding była explicitly shifts the obligation into the past and shows that it wasn't fulfilled. While powinnam zareagować can mean "I should react" (present/future) or "I ought to react", powinnam była zareagować specifically means "I should have reacted" (but I didn't).

Why is the past tense word była used here instead of byłam, since the speaker is saying "I"?

The word powinnam already contains the first-person ending -m. In this structure, the personal ending attaches to the powinien- part, and the helper verb być stays in the third-person form that matches the subject's gender (feminine singular była). For a male speaker, this would be powinienem był.

Why are zareagować and uprzedzić in the perfective aspect here?

The speaker is referring to specific, one-time actions that failed to happen in a particular past situation. Perfective verbs are used because the focus is on the missed completion of these events, not on an ongoing process or a repeated habit.

Why is the pronoun cię placed before uprzedzić rather than at the end of the sentence?