Well, this happened to me as well. With a mother & daughter pair even though they were bonded...
I tryed putting some all natural healing cream on it but buttons (the hurt guinea pig pictured above) scratched her nose & it bled again.
So I left the bite/scratch alone, keeping a close eye on it. It never infected - otherwise I would have gone to the vet. But it healed good and quick.
I left the pair together all the same, even though Buttons was hurt. I think she was biten/scratched by Nelly (mom) because of the lack of space and Buttons was just being a bad girl.
Keep a close eye on your guinea pig. And if the cut/bite gets infected go to the vet.
If the 2 guinea pigs seem to be all right together otherwise, I'd leave them together.
Also, you may want a larger cage (depending where they are living right now - when the bite happened to Buttons, they were living in a pet store cage)
Hope I could help!!