I'd love to battle Leaf =), rename her as Green/Blue ofcourse (Forgot the name of Viridian City Gym Leader in HG/SS, it's Green isn't it?)
Now, what would her team be? I'd think of her as a prelude to battling Red, like you'd battle her on Seafoam Island or at the entrance to Viridan Forest or something. Then you could battle her and Red in a tag battle after you defeated them both seperately.
Team 1:
-Lv.72 Wigglytuff
-Lv.71 Espeon (Since Red doesn't have it anymore =P)
-Lv.74 Meganium
-Lv.76 Ninetales
-Lv.75 Blastoise
-Lv.77 Clefable
Team 2 (Duo Battle with Red):
-Lv.92 Espeon
-Lv.95 Wigglytuff
-Lv.97 Blastoise
Red's would be:
-Lv.99 Pikachu
-Lv.95 Venusaur
-Lv.95 Charizard
That's what I think, anyways.