I mean, she slept with the MC the day they met... so this all started due to her being a slut. Though she isn't really a slut, my guess is that she simply doesn't see any worth in her own self, so sleeping with anyone who wants her isn't a problem. She has no reason to live, so she has no reason to take care of herself, so sleeping around and getting in danger is ok for her (though she did rope mc in in chapter 3, so could be a slut lol)
And yeah, the childhood shit being guy would be a mediocre twist, but a twist nonetheless