"Am I forcing my morals onto her?"
The answer is "No" kid. She's not right in the head due to her neglect, but that's her parents' fault, not her's.
That being said, this might just be me, but the recent developments haven't been as much of a shock, but that's probably cause it's following the same pattern of "Otaku steals Gyaru from her neglectful boyfriend" hentai, but just a lot more drawn out. Of course, with a lot more serious in-universe implications, depending on how old this Senpai ends up being.