"The child Ilham has died as a martyr due to the abuse of children's lives in Yemen," the non-governmental organization said.
Her death was a "flagrant example" of the results of opposing the ban on child marriage in Yemen, which was leading to "killing child females," it said.
The marriage of young girls is widespread in Yemen, which has a strong tribal structure.
The death of a 12-year-old girl in childbirth in September illustrated the case of the country's "brides of death," many of whom were married off even before puberty.
Controversy heightened in Yemen recently over a law banning child marriage in the impoverished country through setting a minimum age of 17 for women and 18 for men.
Thousands of conservative women demonstrated outside parliament last month, answering a call by Islamist parties opposing the law.
A lesser number of women rallied at the same venue a few days later in support of the law, the implementation of which was blocked pending a request by a group of politicians for a review.