Girls can be like that... instead of having one BIG fight about who's in charge, they can bicker their whole life.

There are no garanties it will not happen again, and bloodshed should not be accepted but there is not much you can do about , really.
Supervise them, let them spend time together only when you are close. Then, if it seems OK, try putting them together again and hope for the best.
I keep my oldest girl in a separate cage over night sometimes when she seems too stressed out by the young ones. If I fail to do so, one of my small girls will probably get bitten and I feel like the worst mom in thew world for not keeping her safe.

Other days they are friends, sleep together, groom eachother and so. IOn a way it would be easier if they fought all the time - that way I would know for sure...
But rats do heal well, just keep the wound clean and it should heal in a few days.