copying my post from 6 months ago
"okay im not sure the exact trigger but i finally got it.
i had her facing the train door and gave her headpats and stroked her cheek until orgasm.
I did have all achievements by this point, i think you need to have had sex with her before. on a new day give her headpats/caress her cheek before doing anything else"
This is how it triggered for me.... so could try that. Otherwise its still unknown