How old are your hamsters? Well, there is only 1 solution and that is separation. Some Winter Whites tend to be very territorial and I see this happen to females more often than males. Yah, they will be ok today when younger but once they reach 5 months old or 6 months old... they will start to be a bit more territorial and can get moody and aggressive if another hamster is around. Be it sibling or partner, they will start to fight. Quite common. Some would fight badly, some would squabble.... some won't show so much aggression so they tolerate each other easily.

The mistake people normally do is buying a small cage..... For 2 hamsters, you really need a big cage. Get a 50cm cage or tank..... they need space. Habitrails and whatever fancy cages with no 2nd floor or 3rd floor are too cramp for 2.... even those small but tall ones are not suitable. Critter Trail 2 and whatever cage that has 2 storeys are better but make sure it is more than 40cm in length.