They said we learn from people—and it was true.
In Penny's first life, what Nathaniel taught her was that enemies could smile, laugh, wish you good luck, and call themselves friends without a problem. The pain, disappointment, and rage Penny felt for her family were as painful as it could get, but this guy brought a different kind of pain.
After all, her family should've been her pillar of support, but they never imposed themselves like that. From the beginning, they didn't like her. Therefore, even if they scolded her and never appreciated her, it was almost a given that they'd do such a thing.
But Nathaniel?
Nathaniel posed as a real friend and someone she could trust. He acted like he was her only ally, like he was the brother she never had. That was why, after learning the truth behind her downfall, it broke the only piece that was keeping her together.