Len is other assistant. She can't take Luna's place.
Len-
- Find Mason and Melanie in apartment 201 while they having sex. Talk to them until Melanie tells you to call Len for dinner. After that capture the ghost and you should be able to get access to apartment 101.
Rachel - She can replace Luna but you will need two quest done. First, getting Wendy as assistant and completing thunder girl quest.
- In apartment map, see if apartment 201's window has no light. If it's lit, leave and come again.
- If lights are off go in the room and find a portal at the end.
- Going through the portal you will be teleported to a new room with a guy reading something on bed. Go out and talk to girl outside until bottle in her hand disappears.
- Go in the room again and talk to lady in the kitchen. She will say she feels dizzy. After that to the other girl from before.
- She will go inside and began having sex with husband of tall girl. You can unlock their animation by interacting with them.
- Now go to room next to it and you will find the tall girl on the bed. Try having sex with her until the boy hits you.
- After the cutscene, go out to meet Regina and follow her instructions.