。
She got a lot better.
Literal
She [topic-は] very lively became.
元気 is one of those untranslatable words covering 'healthy, energetic, lively, in good spirits.' 元気になる ('become well') can mean physical recovery from illness, return of energy after exhaustion, or just emerging from a low mood — context picks the right reading. The ~になる pattern is the standard 'become X' construction, with な-adjectives and nouns linked via に before なる; the parallel for i-adjectives is the く-form (大きくなる 'become big').