Forgiving the Bennets, Nina, the Cortez family, and the world was never part of Penny's plan to begin with. She died so unjustly, but before that, she had already endured unimaginable pain—pain so deep that even the world couldn't bear to carry it.
If the world had been just a bit more reckless and let her be reborn as an adult, she would've cut all ties with everyone. She would've led a different life, one where all the people who had caused her pain weren't in it. It wouldn't have mattered if she had to live in seclusion—she had lived in seclusion before. The only difference would be that this time, she would live alone on her own terms, not because no one wanted her in their lives.
But she was reborn as a child, at the most vulnerable time of someone's life. So, she had no choice but to live and make her life better with so few resources.
Did that mean her pain went away? Not in the slightest.