Oh crap, I now understand what's happening, basically when you press space to go forward you can accidentally go to sleep again, since you have less stamina when waking up.
Regarding who of them should appear during the night, they have a pool of chance that depends on how much time you have ignored each girl, technically if roxy appears the other girls will have a higher counter and they should appear instead, but if you get "unlucky" she will appear.
I will chance the day threesolds in the upcoming patches, depending on how players react to it.
In any case, thank you for reporting the issue!