Is the baby really the girl's child? I don't think she can get pregnant without anyone noticing. I also think it's kinda fishy that the story didn't say anything about the glass girl going absent for a few months to hide her pregnancy unless there's a plot twist or some sort.
@hikufalafel There is a thing called "pregnancy denial" where the future mother isn't aware that she is pregnant and so her belly doesn't grow at all even when the baby is about to come.
So, it might have happen to her, perhaps.