NITA BHALLA A Tanzanian law that bans pregnant girls and teenage mothers from attending school is being challenged in Africa's top rights court by an international women's charity, which said the "discriminatory" rule trapped girls in poverty. Equality Now said it had filed a joint petition with a local partner at the African Court on Human and Peoples' Rights against the Tanzanian government on Thursday after years of campaigning unsuccessfully for the ban to be lifted. "We have advocated for more than three years for the government of Tanzania to lift the ban on pregnant girls and adolescent mothers accessing…