。
She really enjoyed the party.
Literal
She [topic-は] party [object-を] very enjoyably enjoyed.
とても楽しく楽しんだ has a faintly redundant ring in Japanese — 楽しく ('joyfully, pleasantly') is the adverbial form of 楽しい, and 楽しんだ is the past form of 楽しむ ('enjoy'); both are built on the same root 楽 ('pleasure'). A native would more typically say とても楽しかった ('was very fun') or パーティーを大いに楽しんだ ('thoroughly enjoyed the party'). The doubling of root 楽 lands as overstated and slightly textbook, the kind of phrasing that appears in translated material where 'enjoyed it very enjoyably' has been mapped a bit too literally.