The 26-year-old mother died on Friday morning at a hospital in central Kampong Chhnang province, a day after the infant perished following the accident, local deputy police chief Chhay Khemrath told AFP.
Her son and another daughter, aged five and eight respectively, were also badly stung by the insects and have been transferred to Phnom Penh for hospital treatment.
"The Vietnamese family went fishing and tried to tie their boat to a tree, but it hit the hornets' nest triggering the attack," he said. "The father tried to get away from the tree, but the engine failed."
In a separate case, an 11-year-old Cambodian boy died on Wednesday after being stung by hornets a day earlier in Kampong Chhnang province, according to local media.