Maria Hill was Nick Fury's second in command because she was very good at her job. She looked after the Avengers while working as the Deputy Director of the world's greatest intelligence agency. She even saved Natasha, Steve and Sam when Hydra tried to take them out. She kept an eye on Coulson and his team. She worked at Stark Industries after she helped bring SHIELD down. Maria Hill is the reason half of our beloved superheroes are even alive. She doesn't need superpowers to keep up with the Avengers.