Local government official Sakib Al-Rabby said the bride was not with the group when the incident occurred on Wednesday in Shibganj in Chapainawabganj district.
Al-Rabby said the group had just left their boat to take refuge because of the thunderstorm when they were struck.
The area is about 150 miles (245 kilometers) northwest of Dhaka.
The annual monsoon is currently underway in Bangladesh. Each year more than 200 people, mostly farmers in their fields, are killed by lightning.
Experts say worsening air pollution is contributing to an increase in the frequency of lightning strikes in the country.