"knows"? No. Its not shown that she knows of the room or what is behind the door... she knows that there is a locked door, and tells the MC "ask Bella" because she doesnt kiss and tell... thats all there is.
Of course Jill could know exactly whats up, but she doesnt show that in the scene you mentioned... its totaly vague and can mean anything. I dont think she would hide that anymore at this point (especially on her path of course), if she knows whats behind the door and it is something Bella needs help with or for, she would have told MC "we need to talk with Bella about this and that"
Again the "I would called for help" sentence out of episode 3 is hanging in there, and not without reason... If Bella needs help, and Jill knows everythign about that, that would be very weird.
And no it doesnt happen in RL... because its impossible to take care of person, no matter in what state, behind a locked door and hide that for numerous people visiting your home, going in and out unbothered, and you cant leave yxou home for several days. Bella sleeps over at MCs, goes on skiing trips and what not, all the while there is a living person locked behind a door... sure... that happens in RL... no, really not. Kiddnapping or some sort, yeah that happens, but not behind a door close to your bathroom while numerous people are going in and out.
And so on and on... point is, its ridiculous to think that there is a living person behind that door, and if there would be... DPC is batshit crazy and an idiot. He is, but not that moronic.
