。
She let me know about her decision.
Literal
She [topic-は] me [to-に] self's resolve [object-を] informed [for me-てくれた].
自分 here is the reflexive pronoun referring back to the clause's subject — 彼女 — so 自分の決意 is 'her own decision/resolve.' 自分 is the standard way to say 'one's own' without specifying the person; the referent is whoever heads the clause. 決意 is more weighted than just 'decision' (決定): it carries the sense of a resolved commitment, something one has steeled oneself to. The ~てくれる auxiliary on 知らせる adds the gratitude layer — 'she did me the favor of letting me know.'