The following “events” trigger me
1. Don't turn around in the shower -> Kayla goes for physical contact.
2. Don't turn around in the shower 2. -> Kayla stays away.
3. Turning around in the shower -> Kaly kisses Jenny
4. Don't turn around in the shower 3. -> Kayla becomes more offensive and promises that things will continue at night.
If nothing triggers you, try visiting her at night. Either when she is sleeping or masturbating. Jenny will open up to her more and more until they make out with each other. From there it's just a test of patience.
If the progress is far enough, you have the opportunity to make out with Kayla in the shower and at night, repeatably.
The fact that you can visit Kayla at night is extremely rare. Therefore, I made changes to my save to trigger the visit event or mastubation more often. Otherwise the progress takes forever.
I would say a mixture of everything. Important: shower and Kayla's bedroom in the evening.
If you can't find her in her room in the evening, she might be in the kitchen or living room. Then first interact with her there. But as I said, without adjusting the save, the progress takes a very long time in the evening.
You should also interact with Kayla when she's gaming, drawing on the computer, or watching porn to increase the chances of you catching her sleeping or masturbating.