@Hessa, the exile is historically inacurate, I couldn't find anything about So's exile anywhere, both SOGC and ML:SH have added the event for the thrill of the drama, much like ML:SH added the scar on So's face.
@Hanah, I honestly cannot explain the Queen's feelings toward So, but I think much of the hate comes from self despise and fear, as she was the one to leave the scar on his face. She was obsessed on seeing her son as the next king and as Yo was the oldest, her affection naturally went for him, as he was the next in line after Mu, and So was just another child, until she scarred her face, after which he was the reminder of how she lost her place in the King's eyes, and later that she couldn't stop his marriage spree and countless princes being born from those marriages (of course, there is also Jong, for whom, I think she was just a mom, as he was not close enough in the line to aspire for the throne (but of course, we see her cross that line also, when she was making Yo abdicate in favor of Jong, while Yo was dying!), from the time we saw them together, she cared deeply for him, and was always afraid that So will hurt Jong as a revenge to her for scarring his face and exiling him, one more proof, that she was more afraid of what he might do because of her actions toward him.