。
She has also become a full-fledged woman.
Literal
She [also-も] full-fledged [possessive-の] woman became.
一人前 (いちにんまえ) literally means 'one serving/one person's portion' but figuratively means 'fully fledged, independent adult.' It's a common expression for someone who has matured and can stand on their own. Combined with になった (became), it marks a completed transition.