。
She celebrated my success.
Literal
She [topic-は] my success [object-を] celebrated [for my benefit-てくれた].
祝う ('to celebrate, to congratulate') takes the celebrated event or person with を. With the benefactive ~てくれる, the celebration is framed as something done for the speaker's benefit — 'celebrated [in honor of me / for my sake].' 祝ってくれる carries the warmth of someone going out of their way to mark another's good fortune. Common around birthdays, graduations, promotions, and other milestones.