。
She forgave me for breaking the mirror.
Literal
She [topic-は] mirror [object-を] broke fact [object-を] forgave-(for me).
Two grammar pieces work together. ~たこと nominalizes the past action ('the act of having broken') so it can serve as the object being forgiven. ~てくれる marks the favor as flowing inward — the speaker is the beneficiary of her forgiveness, even though the speaker isn't named. This is the giving/receiving system at work: the choice of くれる over plain 許す signals that her forgiveness is conceptualized as a gift to me. Without the ~てくれる, the bare 許した would feel oddly impersonal — Japanese strongly prefers marking inward favors with the giving/receiving system.