。
She gets up the earliest of anyone in my family.
Literal
She [topic-は] my family [in-the-中で] number-one early gets-up.
一番 ('number one' / 'most') paired with an adverb forms the superlative — 一番早く ('earliest, the most early'). The setup ~の中で ('among / within') sets the comparison group: 'within my family.' This is the standard Japanese superlative pattern: [group] の中で 一番 [adjective/adverb]. Note the absence of a が-marked subject before 早く起きる — Japanese omits the subject (彼女) by relying on the topic-は from the start of the sentence; the verb is hers throughout. 早起き (waking up early) is culturally praised in Japan — 早起きは三文の徳 ('the early riser gets three mon's worth of profit') is a classic proverb.