Tā cóngxiǎo jiù zhēngqiáng-hàoshèng, bùgān rénhòu.
She's been fiercely competitive since childhood, never willing to fall behind.
Tips
history
Recorded in Qing novelist 文康's 《儿女英雄传》 chapter 35: 任是争强好胜的,偏逢用违所长 - even the most competitive types end up forced to use their strengths in the wrong places. The phrase has lived in Chinese ever since.
usage
Slightly negative tilt - implies excessive ego, not just healthy ambition. For a positive flavor try 力争上游 (strive upstream) or 不甘落后 (refuse to fall behind).