She looks perfect just casually running her hand through her hair.
ーShe looks perfect just casually running her hand through her hair.
「彼女は無造作に髪をかきあげるだけでキマる」
to run one's hand through one's hair で「髪をかきあげる」と言えます。
この場合の「キマる」は She looks perfect のように表現できます。
「無造作に」は casually を使って言えます。
ご参考まで!