。
Her hair turned white from all the hardship and worry.
Literal
She [topic-は] hardship and worry [out of excess of-のあまり] hair [subject-が] white-became.
~のあまり attributes the result to an excess of the preceding feeling or condition — here, hardship and worry. The body-as-subject construction 髪が白くなった ('hair became white') keeps 髪 in the が slot while the change-of-state happens to it; this 'larger experiencer (彼女) — body part as subject (髪) — change verb' frame is one of Japanese's standard ways of describing physical changes that happen to a person. The image of hair turning white from worry is a cross-cultural cliché — the Japanese phrasing here is straightforward and not metaphorical.