。
She cooked fish for me.
Literal
She [topic-は] me [to-に] fish [object-を] cook-did [for me-てくれた].
料理する is one of those highly productive 'noun+する' verbs — 料理 ('cuisine, dish, cooking') becomes a verb when paired with する. Japan's relationship to fish is deep and varied: it sits at the heart of traditional Japanese cuisine, from sashimi and sushi to grilled (焼き魚) and simmered (煮魚) dishes. The auxiliary ~てくれる folds in gratitude — 'she did me the favor of cooking.'