Tang Moyu was seeing the mother who raised her in a different light now. She could now clearly see the hatred in Zhang Wuying's eyes, the same one that she tried to ignore before. The woman clearly hated her to the bones and wouldn't hesitate to hurt her if she gets a chance to do so.
Before, she would be upset and would be in tears after hearing such demeaning words from Zhang Wuying. However, now, she could only see it as an attempt to subdue her, to control her by making her feel bad about herself. After knowing the truth, Zhang Wuying's seemingly unfounded hatred simply made more sense now.
Tang Moyu lowered her eyes, not because Zhang Wuying was right, but because she was trying hard not to let her see the storm in her eyes. All her life, the empress questioned why no one loved her, why no one cared for her when every child she had ever met had a better relationship with their parents.