Thought there was a mistake in MC explanation but it makes sense, the MILF was raped and brainwashed through the course of the game, she dissapeared half into it because the bad guys likely decided to keep her with them 24/7.
She can't be saved because the devs made she start to fall from before the prologue even started.
Is even possible she was corrupted early and used to get information from the villains.
If anything is weird MC knew where to find the hideout where it happened, maybe there was some flavour text in the game, or when the milf appeared as a enemy she explained what happened before attacking in detail.