
We don't know if she was telling the truth about her assault or not . To me it seems she wanted to gain Bum's attention first through seduction and then sympathy. She doesn't care about Bum's emotions and one day she just appears on the door trying to destroy Bum's relationship with his lover . Of course Sangwoo was and still is AN ASSHOLE but it is consequence of Her acction that will affect Bum . But on the otherside it's also Bum's choise to be with Sangwoo and if anything happens it's his responsibility for his (maybe) wrong choise .
I'm gonna go crazy!!
This webtoon is such a mess ! I don't even know on which side I am (╯°Д °)╯╧╧

She didn't know she would have met Bum that day, Bum noticed the bruises like it happened during high school, when his father raped her. She could have put Bum's life in danger but i don't think she meant it, it's not her fault Sangwoo's is a murderer and thinks of Bum as his possession.
As for Bum's choice, it's just partially his. Bum is mentally ill ( he's canonically BPD) and he thinks nobody but Sangwoo can love him, but it's also true that Sangwoo destroyed every chance for him to have a normal life, forcing him to kill.
It seems Bum borrowed money for Sangwoo's birthday present. The Girl is an asshole (︶︿︶)=凸