Milord She was old enough to just move out. She even had a job, so there's no way he could have abused any power over her, since he hadn't any.
If she wasn't ok with it she could have just said arrividerci, pack her stuff and be gone forever.
Maybe she got used to it, maybe she found comfortable with it - who knows.
But in the end it's her decision. I can't force someone to do what I would have done, neither can you.
You can advice, try to convinve them - but in the end, it's their decision