Dream Girl has the ability to see the future - typically in her dreams - and has the distinction of having left the Legion proper to join the team of Legion rejects known as the Legion of Substitute Heroes, where she honed her abilities - both in terms of accuracy and how far she could see into the future - before returning to the Legion, where she went on to serve a term as the leader of the team.
Back in 1976 when he was serving as writer (for the second time) of the Legion, Jim Shooter wrote the following note about Dream Girl:
Dream Girl is dumb. Her power is more or less hit or miss in value (though it is
always accurate) and I'm sure her main service to the Legion is in her quarters
after dark. She needs constant reassurance of her value, and since her Legion
career has been less than stellar, the only way to get psychologically stroked
is to allow herself to be physically stroked. By anybody.
Yikes. For more info about the Legion - and more of Shooter's notes - see this recent article at Comics Alliance.