Ghost Girl was member of the Future Family of earth 7. She died along her teammates when the Gentry attacked her universe. leaving her in a vaporous, dematerialized state, joined to other ghost of that world in a similar state.
As earth 7 was an Essential version of earth 8, it is very possible than a Ghost Girl analog exists in earth 8 as member of the Future Family of that world.
Ghost Girl is the Invisible Woman equivalent in the Future Family team.