Risa didn't tie up her hair and let her hair down naturally.
Risa's hair isn't tied up and is hanging down naturally.
「リサは髪を結わずに自然にたらしています」の英文を2つ紹介します:
[Risa didn't tie up her hair and let her hair down naturally.]
tie up one's hair = 髪を結ぶ
let one's hair down = 髪をおろす
[Risa's hair isn't tied up and is hanging down naturally.]
この文は受動態なので、(be) tied up を使っています。
hang downは「たらしている」というニュアンスです。
また、どちらの文に「自然に」のnaturallyを使っています。