It's not the first time someone has written this, now I think she is Bisex to make sense of the game, but at the moment there is nowhere written that she is bisex. What we do know is that after the experience with Kim she started dating the future teacher with whom she is now engaged / married. Where did you read that she is bisexual? What if the purpose of the game, of the MC, was precisely to open the mother to the world of bisexuality? The fact that she has 2 children is no proof of bisexuality, when it comes to time travel anything is possible. When the MC and Kim meet her she is depressed, she may have found out she is pregnant with the stupid boy we met in the woods, and here is the first daughter justified, the MC may have been adopted, or even his own son.