In Pokemon white after you beat the game how do you re-fight bianca?

Question

I can fight cheren but I can't fight bianca.

Answer 1

To Re-fight Bianca, you must beat the game twice then on weekends go to Professor Junipers lab and talk to her.

Answer 2

After you defeat Ghetsis, you meet Cheren on route 4 to allow his rematch, but you might find Bianca hasnt turned up anywhere.

If you defeat Alder Once, she automatically appears in Professor Juniper's Lab in Nuvema Town. The dumb thing is, unlike Cheren, you can battle her once a day, but only on weekends. On weekday she is looking through her pokedex in her house.