。
She memorized her lines incredibly fast.
Literal
She [topic-は] her own lines [object-を] extremely fast memorized.
せりふ (台詞) means 'lines, dialogue' in the theater/film sense — words a performer speaks. The kana spelling せりふ is common in modern usage, though the kanji 台詞 (or 科白) is also seen. 非常に ('extremely, very') is a Sino-Japanese intensifier with formal flavor — sharper than とても. 早く is the adverbial form of the i-adjective 早い ('fast, early'). 覚える ('to memorize, learn by heart') with the past tense reports the completed feat.