In some fanfictions, it could be because Peter has a pure heart. Just like in the MCU, only those worthy can lift Mjolnir. Peter might have proven his selflessness and heroism in a particular situation, which made him worthy enough to lift Thor's hammer.
Well, it all started with Bruce Banner. He was a brilliant scientist. He was involved in gamma radiation research. One fateful day, there was an accident during a test. The gamma radiation he was exposed to altered his DNA. As a result, his body now has this dual nature. When his emotions, especially anger, reach a certain level, he morphs into the Hulk. The Hulk is like a primal force, with superhuman strength, and he's not really in control like Banner is in his normal state.
She-Hulk became a Hulk because of a special circumstance involving a blood transfusion from Bruce Banner. This caused her body to react and gain the Hulk-like abilities. It's a unique origin story that sets her apart in the comic universe.
She-Hulk gets her powers through a blood transfusion from her cousin, the Hulk. This transfer of gamma-irradiated blood gives her the ability to transform into She-Hulk.
It happened through a combination of events and character development. Hulk started to gain more control over his emotions and powers, which led to the transformation into Professor Hulk.
If Hulk and She - Hulk are having a baby, their relationship will surely change. They might become more protective of each other. For example, Hulk could become more gentle around She - Hulk, showing a side of him that others rarely see. And She - Hulk might rely on Hulk more for emotional support. Their relationship could also face challenges. They may argue about how to raise the baby, considering their different personalities and ways of dealing with power.
Their relationship could be portrayed as a mentor - mentee one, where She - Hulk looks up to Hulk for his experience in dealing with his powers and the world of superheroes. Another way is to show them as rivals, competing to see who can save more people or defeat more villains in a given time. This would add a new dynamic to their interactions.
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.