I don't think Mia ever hated Leana. She did have crush for the emperor before Terrier beat some sense into her and send her off for the monastic tour. All because of Lehman's evil words. If anything, she felt sympathy for Leana and disdain towards the emperor after knowing his bad initial treatment to Leana.
At the very least she didn't turn to be the annoying evil protagonist naïve teenage girl that we all love to hate.
Did people forget mia is like that because of viceroy? (Is that the name of the blonde guy? I forgot)..She felt guilty for liking leanna's husband but viceroy said it's okay since she's fated to be with the emperor, viceroy also told her the emperor and the empress don't love each other or something + the queen's position is still vacant and mia has the right and fated to be the queen, so she stupidly believed it
Are they making us forgive Mia for hating empress and being in love with a married man only bcs she learned what happened at the beginning of their marriage?