Please could you give us a lot more background to the situation. We can’t yet advise whether this is a normal hierarchy process during a brand new bonding (ie within the first two weeks) or whether they’ve been together for longer and the bond is actually failing.
How long have they been together?
Did you bond them properly in neutral territory?
How big is your cage? It needs to be 180x60cm for three sows
How old are they all?
How long have you had the first two before you tried to add in Chilli?
Have you checked they are definitely all sows?
Is she actually biting and breaking the skin/ causing injury?
Is she actually ‘attacking’ - ie rolling around in a fur ball fighting with her? (Such fights are less common in sows)
If so then the bond is never going to work and they will need to live separately permanently.
Nipping is what normally occurs. It lets the underpig feel the teeth but without injury, it is a gesture of power. This is not of concern and is part of normal bonding while they set up their hierarchy.
The fact is though that you can’t make piggies like each other. Adding a new piggy to a bonded pair on spec always comes with a risk of failure if they don’t want the new piggy with them. We do see cases where adding a new piggy disrupts/breaks the bond between the original two.
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
Adding More Guinea Pigs Or Merging Pairs – What Works And What Not?