“It is clear that I have gone through unbearable mental suffering after my son abruptly died on a school excursion,’’ the Yonhap news agency quoted her as saying.
Further lawsuits from other bereaved relatives are expected.
Believed by authorities to have been overloaded, the Sewol sank on April 16 carrying 476 passengers, mostly school children.
At least 292 lives were lost, and 12 people are still missing.
Earlier this month, the trial of the captain, two officers and the head engineer began in the south-western Korean city of Kwangju.
They are accused of having done nothing to rescue the passengers, and could face the death penalty if found guilty. (dpa/NAN)