Captain America would be a great addition. His leadership and moral compass could guide Hulk and She - Hulk when they face difficult decisions. And his combat skills could come in handy during battles.
One key element is the power dynamic. Given their super - strength and large - scale capabilities, how they interact with each other in terms of power usage is often explored. For example, in some fanfictions, they might have to hold back their strength when being affectionate.
Sure, She-Hulk is related to Hulk. Jennifer Walters, aka She-Hulk, got her powers because of a blood transfusion from her cousin Bruce Banner, who is Hulk. This connection is a key part of their storylines in the comics.
One idea could be a team - up story. Batman and She - Hulk have to work together to stop a powerful villain who is causing chaos in Gotham City. Maybe the villain has some sort of technology that is affecting the citizens' minds, and She - Hulk's strength and Batman's detective skills are needed to figure out the source and stop it.
In many comic versions, She-Hulk gets her powers after being exposed to gamma radiation, similar to the Hulk. But the details and circumstances can differ in different story arcs. Sometimes it's due to a scientific experiment gone wrong, or a deliberate attempt to gain powers.
She-Hulk became She-Hulk because of a unique set of circumstances. Bruce Banner's blood, with its gamma radiation, entered her system during a medical emergency, and that's what caused her to turn into She-Hulk. This event changed her life forever.