when checking the safehouse and cassie isnt there, go to the apple tree first to see if shes picking apples.
also how do you give gin a maid set? i cant get that interaction.
You need to progress his training until you have only 2 options to train him
If you haven't given the maid costume to Gin yet, the first option will allow you to, provided you have the full set.
Also, yes you can check the apple trees for Cassie, and the milk farm too just to be sure but running all over the place looking for other places she might be in is a bother so I just preferred to save before checking the lake and reloading if she's not there.