Relationship with Yuna has nothing to do with Kaede
Let's start from the beginning:
- during Friday party you can gain impression points (having high base stats help gaining them and a little drunkness, like 2 or 3 points), then at the end of the party you have a chance to convince kaede for a sleepover (high base stats + impression)
- if she agrees, then she will be in yunas room only that same night rights after the party, on the floor, right side of the room in a sleeping bag (hard to miss)
- afterwards she will apprar in yunas room everytime it rains at night (there's 30% chance for the rain to happen naturally, or you can use 'rain stick' in the morning to make it 100% only for one night)
- if she isn't there after the party - that means you haven't successfully convinced her to stay, you have to I wait for the next party and try again
TL;Dr
- high stats + impression + a little drunkness - convince kaede to stay
- she's in the room immediately after party and when it rains at night (30% chance, use rain stick in the morning to make it 100%)