Best order seems to be:
-Go to the Bar and agree to have sex with Leilani. I'm not sure if dialogue choices matter but I told Anna that she did ruin the vacation when she catches you.
-On the next trip, keep reloading your save on Friday when visiting the Beach until you get the event where Anna forgets her sunscreen. This is where you'll meet Freya.
-Do the same thing the following week until you get the follow-up event where Freya attempts to hit on Anna.