。
You should have apologized to her.
Literal
You [topic-は] her [to-に] apologize [should have-べきだった].
~べきだった (should have) expresses regret over an unfulfilled obligation — the apology didn't happen but it should have. 謝る (あやまる) is the standard verb for apologizing, less formal than 謝罪する. 彼女に marks the person who should have received the apology. The sentence is a direct criticism or regretful observation about past inaction.