。
She gave me something wonderful for my birthday.
Literal
She [topic-は] my birthday [on-に] very wonderful thing [object-を] gave.
くれる is the inward benefactive — the give-verb used when something is given to the speaker or the speaker's in-group. Distinct from あげる (the speaker or in-group giving to others) and もらう (the speaker receiving). Choosing くれる here automatically positions the speaker as the recipient without naming them. に on 私の誕生日 marks the day as the temporal point of the giving — 'on (the occasion of) my birthday.'