By Seun Sanni and Temilade Adelaja OWO, Nigeria (Reuters) -Theresa Ogbu took two of her five children to mass on Sunday to celebrate Pentecost, a joyful occasion for a devout Catholic, but the boys came home without a mother. Ogbu, 51, was shot in the head as she tried to escape from St Francis Catholic Church in Owo, Nigeria, where the congregation came under attack from unknown assailants firing guns and hurling explosives. “I miss my mother so much,” said Victor Ogbu, 13. He and his brother escaped unharmed, only to discover later that their mother lay dead in a pool of blood in a church ai…