If there was more than one adult male in with her, that could explain the fighting. Male piggers can get along very well together, but often fight if there is a female present - for who gets to mate with her. As she will have gone in to season right after giving birth, that could have set them off competing with each other. I hope that none of the males got to her before you removed them anyway - just keep her with her bubs now. Hopefully in a couple of weeks their gender will be clear but if not, check with your vet so you can remove the boys at 3-4 weeks.

Here's a great page on biting with lots of advice on how to handle it. http://www.cavyspirit.com/biting.htm It's really important you never hit or punish them because it just doesn't work. A piggy will only bite because it is scared or feels threatened, and by physically hurting it, all you do is confirm it was right to be scared. So next time it will be expecting to be hurt again so will be even more scared and defensive - you earn yourself another bite. Good handling, time and patience is what's needed and I'm sure he will be back to his usual self.

The only thing worth mentioning is that if a usually friendly piggy suddenly becomes reluctant to be held and starts biting, it can indicate they have a parasitic or fungal condition such as mites. These cause them irritation and makes it uncomfortable for them to be handled. If a change in behaviour like this is accompanied by any extra scratching, dry skin or hairloss then see a vet.

Good luck with your piggers!