It'd be hilarious if this got a sequel in which the other girl wanders off again and comes back as an actual ghost, but the first just doesn't buy it.
So you want one of them to die
Not necessarily. Maybe the (hypothetical) ghost was just knocked out of her physical body and is more like a wandering soul. Part 3 could be about looking for the body, only to find it possessed by the actual ghost of a lesbian who never found love. Part 4 could conclude with a comfy human, spirit and sock puppet polycule.