In the end the only reason to even have the choices is to provide some meaning and depth, so you can write better stories. If the only way to get Helen would be to make Mia a prostitute, people won't be happy, either. In that case you may as well write a more fitting story and change the premise.
Having said that, the game won't ever be this dark. Given that they seem to aim for the "good, protected and sexually repressed girl breaks free and wants to learn more about sex and try stuff" it seems more likely that she'll just say "fuck it" and join Helen and MC anyway.
lets be honest, most "episodes" really need a heavy rewrite/redrawn. the fact we get almost no scenes with mia or her mother shows that they went for the bare minimum. and the story make it seems like we will get alot more, but nop, its just a repeat of the same scene.
to call it a disapointment is an understatement...