Honestly, although she does have an obsession with Anna, I feel like she actually likes Sion.
Im pretty sure its already explained the reason she "likes" Sion is because he was the reason why Ahrin can have a moment as a family member in Moon family. He was the link. Without him she was a merely stranger in the house. Her love, happiness, and obsession will always being given to Anna: all her reason to strive is to make Anna looks at her and at one point she even hope Anna would clung on her. She literally having sex and still thinking about Anna. The only reason she cant bang her is because the genre. Change it to yuri and this girl would just straight up kidnap Anna and become yandere herself.
Is the part when Anna pregnant already translated? Because damn that gurl reaction knowing Anna pregnant is imagining her woman would become more dependent on her.
Tho in Ahrin defense this girl truly love Anna and hope for the best life for her. If Ahrin even being yandere and Anna said she would be sad if Ahrin kidnap her Ahrin wont do it just to not hurt her.
This is weird af but honestly ahnri (?) is in love with her step mom like everything she does is for her and the only thing that makes her happy is her. She couldn't give less of a fuck about these men romantically let's be fr. I'm genuinely confused wtf the author is trying to say with this story and honestly i think this should have been a psychological story with less comedic relief