At the news of her lover's death, her heart was thrown into turmoil.
Literal
Lover [of-の] death [of-の] news [at-に] her [of-の] heart [subject-が] was-disturbed.
Here the heart is the grammatical subject (が) of the intransitive 乱れる ('to be disturbed, become disordered'), so the sentence reads as something happening *to* her heart rather than her actively suffering it. The 乱す/乱れる pair is a textbook example of Japanese transitivity pairs.