My storyline... Now that Bruce Banner has some good faith restored in him after he helped saved the world from an alien attack, being able to work with the Avengers, made him realize that he missed his family... So Bruce goes to visit his cousin, Jennifer Walters. On arrival she is shot by some thugs, is rushed to hospital and needs a blood transfusion to live. Bruce is faced with a dilemma, because he knows they have the same blood type but his is gamma infected!! Realizing that she is going to die, he goes through with the transfusion, which leads to Jennifer becoming the SHE-HULK!! You guys can figure out a cool villain now lol...
Jennifer then joins SHEILD, but not the Avengers... This way you expand the universe but not necessarily expand the Avenger line up!!!