I still haven't really pieced together Guk-Hwa's past. It's only been shown in no-context fragments and it confuses the heck out of me. I wonder if anyone has any good theories here.
Something to do with her mother and either her mother's mother or her father's mother. I'm assuming the father's mother. Might have been violence towards her mother. My gaydar spiked when the flashback had her telling a female teacher she was happy because the female teacher protected her and her mother. So maybe a gay relationship for the mother that ended violently.
Someone important to Guk-Hwa tried to kill their self. Or there was a very violent and bloody scene in which she walked in on.
(I just did this from memory, btw, so forgive me if I misremembered).