Maria Hill is one of the many non-superpowered characters in the Marvel Universe. Although they don't make the best action figures, those characters are very necessary. If it was all superheroes then things would get too crazy, especially at SHIELD headquarters. That and we need characters who can die. Try killing off the Hulk and fans will tear you apart. Kill SHIELD Guard #2 and suddenly we're all heartbroken and rooting for our heroes. Don't you dare kill off Maria Hill though. We like her!
Maria Hill is a major component of S.H.I.E.L.D. She was former Deputy Director and commander of the organization. The Avengers and Nick Fury basically call her for every big battle because she's a cool-headed badass. She's not a woman you can shake. Hell ,if you have the respect of Nick Fury, you must be good.