Ok. now that ive fully read this thread (Lol should of done that first).
My best advice is like what everyone else is saying essentially.
Condition them again...only this time, condition HIM to Her, not vice a versa.
you've got to understand a male betta will flare/get excited over all most anything.
like my VT Constantly makes a huge nest just because (From what i can tell) he genuinely thinks the cory cats are females, i say that because hes delivering the exact same attitude as males do when their trying to impress females.
But on the other hand, females are a little bit more picky. i mean, i tried doing 2 breeds at once. like in seperate breeding tanks, with seperate couples, after being conditioned for the same amount of time.
and my current (So far successful) Spawn, when i actually "Introduced them to each other" (Took out the divider) There was NO fin nipping, just dancing and a very little bit of chasing. But the difference was, is instead of actually taking the divider out, i scooped up the male, and put him in the females side of the tank, and then took out the divider, not to put him into shock, but to make him i guess a little bit less aggressive and a little bit less like "Hey this is my home, im top dog" and they were fine, really fun to watch.
But on the other hand, in my other tank, we scooped up the female and put her in the males side, and within 5 minutes max, part of her back fin (like on the end of her body, not below her body, i forget the name xD) got ripped off. and i mean, like a good chunk, enough to scare us and take her out and instantly give up on him.
In my eyes, some pairs are really just not ment for each other.
I'd suggest just reconditioning them and trying them again, and if its as violent as last time, give up on that pair and consider trying a more aggressive female.