#1 Counter the arm bar
In all honesty, Nikki needs to counter the move once or twice before the evolution pay per view to help create doubt that Rousey can actually lock it in on Bella. This also helps take away one of Rousey's most effective weapon and could even lead to her debuting an even more vicious finisher than before.
If Nikki Bella is going to be any kind of threat to Ronda Rousey and her title reign, she needs to be able to effectively counter Rousey's deadly arm bar. Unfortunately for Bella, no one has been able to successfully counter the armbar, which means that she would have to be the first
In the end, there are a lot of ways to make Nikki a legitimate contender to Rousey's title, but none seem as effective as successfully countering Rousey's key move. In fact, it could go a long way in helping the pay per view buy rate, especially since it at least creates doubt in Rousey being able to get the job done.