To the best of my memory, Lucy was not yet at the pool when I triggered this event. Also, I had not advanced Lucy's story far enough to get that sex scene on the pool deck when I triggered the Andrea event. That may be a conflict. However, If you arrive at the pool and you see Lucy stretched out on the chaise lounge, Lucy's H-scene will trigger. You need to talk to Andrea not Lucy.
Again, I would start at 6AM, stay AT the pool on a Saturday and skip an hour at a time until you get the chance to speak with Andrea. While you are looking to speak with Andrea, do not stop to talk to Mom or Lucy. You can revisit those events on another day. Also, in my game play, I spoke with Andrea long before being able to have sex with Lucy. Again, that Lucy event may be a conflict with Andrea's event. IDK for sure. I completed all of the tasks for Daniel rather early on. That was over a year ago by our calendar. Not sure what day that was in game but it was a long time ago.
Apologies that I can't be of better assistance. Adventure ever on, Phat