Okay, that's weird. I did definitely fuck Lucy the first time she asked, but I just don't recall ever seeing any other prompts to continue with her (I kept going down to the hotspring while she was there in the evenings, but all she did was say hello and that was it; similarly when I talked to her in Kali's room, there was an option for Utility Room Sex and that was all there).
Planning to start a new playthrough once you release the next patch anyway, and going to make sure to really get into training them girls as soon as possible; So thanks again for all your efforts, big fan.