I think I did it. I swaped the swimsuits through the week and not on sunday (still each one after their pool day) and I got the text telling me the girls were in my trap.
the problem is I don't understand the hints from little sally afterward on how will I know if my plan worked
- For the "recruit support" way, Little Sally talk about visions, i tryed the sleeping pills to visit Luna in her dreams but I can't use them anymore since i have a perfect sleep schedule.
- For the "act from the sadows" way, Little Sally talk about a pervert that would creep around the school at night, I tryed to talk with Filsh, Hagrid and even miss Ravenclaws but none of them have an interaction about it.
- For the "earn their trust" way, I think I have to meet with the girl I befriended, but I don't know how to meet her since she doesn't tell me anything about it when I sommon her officially, I can't yet summon her unoficially and I can't fly to her dorm since each time I try Marcus doesn't have anything to do there at that moment I tryed flying there at 22h 23h and 00h since these are supposed to be the time when the girls come back from the meeting.
edit : nevermind, i got it, i just had to summon one and ask her about the meeting ...