Heart of Stone(a avengers fanfic)

Katrina Marie Johnson. One of the many girls Tony Stark has brought home. But she's different, they had and actual relationship. But then he cheated on her with Pepper, and she went to work with S.H.I.E.L.D and after two short years, thanks to some secrets she became S.H.I.E.L.Ds best assassin, and her heart turned to stone for everyone other than Coulson, Hill, and Fury. But what happens when agent Clint Barton is comprised and they Avengers initiative starts up? What will happen when she sees Tony again? What if two more Avengers fall for her