why did alice teel bella to see j if she knew it would all work out in breaking dawn?

Alice didnt know what would happen for sure - she couldnt see the volturi's decision so she wanted them to be prepared - for the very worst, just incase. All Alice knew was that they were coming - on a snowy day. Thats all she could see.
So she got Bella to see J to get passports for Jacob and Renesmee to escape - if the Volturi decided to kill the Cullens.
Her visions were not clear enough to tell what was going to happen - so she wanted Bella to be prepared.