Was the change in Soo-Ja's early close relationship with her daughter true-to-life or was the tension between them later plot driven?

I believe it was realistic. Once kids hit the teen stage they rebel and Hana was no exception. She got the bulk of her attention from Min, so she preferred Min. But he also bought her whatever she wanted (where did he get the money, that's what I'd like to know, since they didn't have much). When he wanted to go to America she was happy to go along and leave her mother. Maybe she thought her mother would follow, or maybe not. But Soo-Ja sacrificed a lot for the cause of her daughter, so much she was hardly around to interact with her. All this made perfect sense to me.

I agree with lisag that the relationship is realistic. I still recall the person I was as a teenager and cringe. Thank goodness my parents forgive me for that!

My daughter's going away to college in the fall. She's excited about it and I told her to enjoy these years because, for me, these were the best years of my life. I see her pulling away, suddenly becoming more critical of me and I guess that's natural. The same is true of Hana and I think Soo-ja was a very understanding mother, making sure Hana knew she could do nothing to make her mother stop loving her and not over-reacting to her daughter's drama.