There are many ways you can get infected actually. Even a little prick in the fingertip can earn you a bullet. It was never really explained how exactly she got infected but it doesn't matter - she still was infected.
And about her falling in love. It was said (by Shaw, the "gramps) that she fell in love with Lu Feng because he saved her life once.
oh aww rip queen tysm for explaining
If I'm not mistaken (it's been a long time since I read the novel), it's parasitic species, high degree of proliferation possible. The larvae is already inside her body (you can see in the panel before she was shot, something popping on her forehead, and she realized that too.
omg i just re-read that and wow the detail is crazy tysm
i think they realized the infestation wasn't only at the front of the train, but after doussey, it seems they yeeted almost the whole compartment.
It's very sad actually, Dou Sei was killed by the person who saved her once whom she also loves :")
can someone explain the thing about doussey? like if the infected was only in front of her in the train why was she shot & the thing about her falling inlove that gramps talked about, did she like fal inlove with the infected