Som-i never once acted like Hae Suk. She didn't act like Hae Suk when we didn't know who she was. In the flashbacks,…
Series world building was very inconsistent and a ton incoherent, but they explained why it happened but not why it was trashier LOL!! It was explained something to the effect that b/c her son died, and she was losing herself and was going to kill herself that part broke off and it became this separate manifestation of all this grief she had over her son.