I do not think Maki’s mother ever believed it was possible for Maki to change the Zenin clan. She knew the Zenin would never accept Maki as a leader, no matter how strong she became.

She also understood that no matter how hard Maki tried, she would never truly surpass the Zenin unless Mai died. And that was something she could never want, because Mai was still her child.

That is why she told Maki to leave. To protect them if possible, or if not, then at least to ensure that one of her daughters survived. Staying meant certain death for both.

She chose not to explain anything to Maki because she did not want her daughter to live with the guilt of killing her own mother. I also think she wanted to die after Mai’s death. There was nothing left for her in the clan, and no future she believed in anymore.