Ask her to explain

What do you mean?"

Queen Zereena admits that when she was pregnant and then gave birth to your older brother, she was very happy to become a mother. However, not even a few days after he was born, your father takes your brother away from her and placed him under caretakers so that he can be raised as the proper prince. While she was the queen, your father rarely spend time with her anymore, preferring to spend the nights with other women, including your mother. To make matters worse, your father also prevents her access to your brother, only allowing her to meet him once a month if your father feels particularly generous.

Eventually, all the love that she has for her son, and all the respect she has for your father evaporated, leaving her embittered. She knew that it was wrong, but she blamed giving birth to your brother as the reason your father casted her away. Trying to provoke your anger, she told you that it was her suggestion to your father to send you away because she's jealous of you being allowed to stay with your mother until she passed away when you're 7.

While the admission does annoy you a bit, you don't let it show on your face. "Is that why you seem at lost?"

"Yes. I'm now wondering why I'm feeling angry instead of sadness,"

She is angry with the situation. Her sacrifice all these years is rendered pointless.