Well, Katniss is the protagonist who has been through so much in the Hunger Games world. She is a symbol of resistance. Snow is the antagonist, a powerful and often cruel leader. In this fanfiction, they are likely to be central to any storylines, with their personalities and the dynamic between them being explored in different ways. For instance, their interactions could range from intense hatred to an unexpected understanding depending on how the fanfiction is written.
One interesting plot could be a scenario where Katniss and Snow are forced to work together in a post - Hunger Games world. Maybe they have to deal with a new threat that endangers both their interests.
Katniss would likely become more protective. Her natural instinct to survive would be amplified by the need to protect her unborn child. This could make her more cautious in her actions in the arena, but also more fierce when directly threatened.
She might get angry. Katniss has a fiery side, and seeing Peeta with another girl could trigger that. She could give Peeta the cold shoulder and refuse to talk to him.
Their relationship would likely become more intense. With a baby on the way, they'd have to rely on each other more. Gale might become more protective of Katniss, and Katniss would have to trust Gale in new ways.
Katniss might be initially shocked. Given her own tough exterior, she may quickly try to restrain Peeta without overreacting. She could be more concerned about what's causing his flashback rather than her own injury at first.
She might struggle at first. Katniss has always been a fighter, and motherhood is a whole new territory for her. She would likely be very worried about not being a good enough mother. However, with the support of Peeta and her friends, she would gradually learn to balance her new role. She would also use her strong will and determination to provide the best for her child, making sure they have a better life than she did growing up in District 12.
A post - Hunger Games plot could be that Katniss and Prim are trying to help the children of District 12 who have been orphaned or traumatized. They start a small school or a healing center. Katniss teaches the kids survival skills, and Prim uses her medical knowledge to help them heal both physically and emotionally. This could also involve some challenges from the Capitol - loyal remnants in the district who don't want things to change.