@KappaDvorak you mean the reunion back in chapter 51 ? When Kindaichi ask about "the father" and "it's still ?",she reply by "that's about it", maybe I'm wrong but in my opinion, instead of "she doesn't know the father of her son" like you said, both Kindaichi and her who who is that guy but I guess that guy just,well, doesn't take responsibility (still not sure if it have anything to do with "that event" make Kindaichi doesn't want to solve case anymore like how his mentioned it)
Sorry if I bother you