Nipping means... I don't like that, you aren't understanding me, and I want you to stop it.
Biting is "I'm upset and angry and I'm going to tell you that in plain guinea pig language".
Billie and all her progeny were removed from my herd. I don't do biting animals regardless of the reason. None of my other females bite or nip so why would I keep one that does? Not something I want to encourage.
ANYWAYS some more delving into the situation that I was called about.
1. guinea pig being held for more than an hour, guinea pig is being petted behind the head and nips.
2. guinea pig disciplining another pig, someone reaches in to stop it and gets their hand nipped.
Nipping is not biting. It's a deliberate act of stop what you are doing, I don't much like it but I'm not upset with you. Rather along the lines of a child whining and possibly hitting out.
So how does one deal with this?
1. Don't hold your guinea pig so long without letting it get around and start exploring and just being a guinea pig. Yes it's a small animal, yes it is easy to hold, but you need to let it be what it is... an animal with a need and will to explore and pee and poo. If you aren't letting it do that, then it will complain.
2. Guinea pigs, just like any other animal, will sometimes want to be left alone or want their own space. Just as most folks won't holler at their children for every disagreement they utter but will let their children sort it out...the best thing to do is to let your guinea pigs sort it out. You don't need to intervene unless there is blood drawn.
3. Don't reward the nipping. Calmly pick your guinea pig up, move around with it, get it settled and then place guinea pig back in it's area OR release it to run around a bit. If you immediately release it, you are telling the guinea pig that it's okay to nip and now you get your freedom (reward).
NOW... if you have been less than thoughtful and have kept your guinea pig in your lap too long without giving it regular potty breaks...then by all means, pay immediate attention to your guinea pigs needs. They do need to go pee and potty, so give them regular breaks and let them do that.