Ever since she was a little girl, she has lacked drive/initiative in whatever she does.
She has never had much of an enterprising spirit most of her life.
この場合、私は backward を使って言わないですね。次のように言うと良いと思います。
ーEver since she was a little girl, she has lacked drive/initiative in whatever she does.
「彼女は小さい頃から、何をするにも積極性に欠けていた」
to lack drive または to lack initiative で「積極性に欠ける」と言えます。
ーShe has never had much of an enterprising spirit most of her life.
「彼女は子供の頃から積極性をあまり持ち合わせていない」
never have much of an enterprising spirit で「あまり積極性を持っていない」
ご参考まで！
カナダ 
