"That boy is our last hope."
"No, there is another."

And the green dude was right, there was another, as Ben knew full well. But why was Leia referred to as "the other" and not Luke? Is there a reason that Luke became the primary focus of the future of the Jedi and not Leia, Anakin and Padme's daughter?
Well, apart from Lucas not knowing they were brother and sister until he was writing Jedi...

Luke was the one being watched by a Jedi Knight as he grew,and showed an aptitude with the Force that Kenobi could sense and watch.
Leia was being raised in a normal family by non-Jedi's - even if she were potent in the Force they wouldn't be able to tell it. Remember, Anakin showed his Force abilities in subtle ways - being able to fly the pod, fixing things. Not showy skills like levitating X-Wings, but much more understated ways.

Luke was kept well away from galactic affairs, on a desert planet on the Outer Rim, raised in a hard-working but simple environment with little to occupy his mind but dreams of a more exciting life and the daily chores of the Mositure Farm.
Leia was on Alderaan, on the Hydian Way in the Core Worlds, and as the daughter of a prominent Senator and Queen she was raised as royalty, doing much like her mother had done and entering politics at a tender age. Even at age 19 she was a `known' figure in galactic affairs, and high-profile herself. Clearly her mothers daughter she was headstrong, forthright and determined to free the galaxy from the grip of tyranny through politics.
And besides, if she had shown even a tremor in the Force, Vader or another of the Emperors minions would have sensed it, and dealt with it.

So, when the time came to bring Luke and Leia to the forefront of galactic events - remember, until A New Hope she was only accused of being a "part of the Rebel Alliance and a traitor", her actions in Star Wars confirmed that to the rest of the galaxy - it was Luke who was clearly the one to bring the situation to a head, not Leia. In many ways they were exactly like their parents. Padme/Leia the politician, Anakin/Luke the Jedi Knight.

Makes you wonder what would have happened if Bail and his wife had always wanted to "Raise a baby boy" instead...