Okay, after actually trying to get it, it seems like you need to wait for gin to leave and then not check up on him, then wait for cassie. Cassie doesn't leave right after waking up, so you need to go do something else for a bit and then check in on the abandoned base later. I think you can be safe by checking the apple spot before the fishing spot, but it's easier to just save before going and load if she's not there.
It still took a while though. My routine of getting 2400 from the devil's drink each day ended up letting me buy 1 of each thing in the entire underground mall by the time I got the second visit... (P.S. this isn't the optimal money making strat, gold mine -> pawn shop is a bit less annoying.)