。
She lost her mind from fear.
Literal
She [topic-は] fear [from-で] mind/spirit [subject-が] strange became.
気が変になる literally 'one's mind becomes strange' = 'go crazy, lose one's mind.' The 気 ('mind, spirit, mood') is grammatically the subject (が) of 変になる ('become strange') — same body-or-mind-as-subject pattern in expressions like 身がすくむ ('one's body cringes'). This kind of phrasing scatters the agency — the speaker doesn't say 'she went crazy' as a whole-self action, but rather 'her mind went strange,' externalizing the disturbance.