@ndkwon I wrote the same theory here a while ago about Seju's mom and Won but nobody think that this could be possible lol.
Interesting theory. :)
Even though anything is possible, I doubt it's going to head into an even more complicated story involving Seju's mother faking her death and had been watching out her daughter this whole time. We are talking about one hell of an elaborate plan that requires dumb luck, meaning the bastard brother was so careless to not make sure she's actually dead, bribing people to lie about her death and so on.
Regardless, it'll still be worth knowing more about her mother, most likely through Won parents. And I wouldn't trust the bastard bro's assessment at all that the parents were leechers after money. Knowing how corrupted his mind works, he wouldn't have spotted genuine friendship if it was right under his nose. I expect soon enough Seju will find the closure she needed about her mother and be at peace with herself. I mean that was the main reason why she came to the villa in the first place.
Lol while almost everyone is battling over Seju x Sumin vs Seju x Won, immature vs mature readers, fast pace vs slow pace and here I found none above is as interesting as the death of Seju's mom as well as her close relationship with Won's parents, because it is too obvious now that Won was arranged to work for Seju since a long time ago. There's also a possibility that little Won had met Seju's mom before because:
1. Her parents already got married and became the caretaker couple like Seju's bastard bro mentioned when they were still working for Chahee.
2. Seju said Chahee gave birth to her in a place where she was called a mop (Seoul) yet she was killed by bastard bro in the hotel (Jeju).
3. Seju's old loyal servant (grey hair dude) appeared in chap 119 + 107 seemed to not know anything about Won's parents and Chahee.
=> Chahee was forced to stay far away from Baek family so that Seju could be raised separately by her father, she might have managed to stay alive for a few years after Seju was born.
So just what really happened to her in the villa during the time Seju's in her womb? Also her suspicious relationship with Seju's good brother - Sehyun. I know this sounds ridiculous but just what if her death was faked in order to be safe. What if she went overseas with Won's parents and didn't dare get back because of some unspeakable reasons? What if she's still alive and has been watching over Seju all this time?
Though I don't even believe very much in these possibilities, but whether or not Chahee's still alive, there's surely many interesting things left about her to figure out. And Won to me isn't just a love interest for Seju to move on from Sumin, but she's also like a blind date setup by Seju's parents so that Seju can get to know more about her mother and learn to love herself more after knowing that she wasn't abandoned by Chahee - the mother that should have loved her unconditionally. This is what the sidestory One is for. That Seju's world mustn't revolve around only 1 person, that she's worthy of love and so much more. That a good woman who has everything like her shouldn't just keep her head low all the time.