Ooh that is a tricky one. I'm assuming this was a proper fight with biting and ear pulling rather than just some nose bumping and assertiveness? And who fought who... because you will have a hierarchy of top pig (she should be obvs), middle pig and bottom pig so is it someone challenging for top place or are the two underpigs scrapping it out? How long were they living as a trio, how old are they and would your plan be to get a fourth to make 2 pairs or to have a pair and a bar-neighbour.
When I ended up with two pairs it was always Zara, bless her, who was intolerant of anyone but her friend Louise. And as Louise liked her too it made it an easy decision. George was eventually paired with new addition Flora. If I'd put feisty Zara alone to look for a new companion I'd still be looking now because she was a gladiator!