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Did you introduce her properly to the herd using totally neutral territory (ie did you remove all the piggies and put them somewhere else for them to meet her) Or did you just put her straight into their cage?
This could make a difference on whether she has actually been rejected - if you just put her into the cage without the proper neutral introduction for several hours then it can be seen as a territory invasion and cause this kind of behaviour without her actually having been rejected. Ears can get ripped by a misplaced swipe rather than a deliberate act.
The other piggies will be sure to put her right at the bottom of the hierarchy so you will see dominance which can look aggressive but actually isn’t. Babies, generally speaking, are accepted as they cannot usually challenge the hierarchy - it’s possible (although you don’t say) that the three who are potentially having an issue with her are the three at the bottom of the hierarchy so they are making sure she stays at the bottom and their places in the hierarchy remain intact (the bottom piggy prior to the baby’s arrival won’t want to be usurped by her). It takes two weeks for them to fully settle the hierarchy.
As a bond comes down to compatibility, if they genuinely do not like her and don’t want her in the herd, then she will never be accepted so waiting until she is bigger and trying again won’t help. If they definitely do not want her, it means that you will need to split your herd (or get her another piggy to have as her own friend) so she has (at least) one other piggy in the cage with her and you will need to have two separate cages permanently.
Equally as she is under four months of age, she should not be alone now so removing one of the other piggies and putting them in with her now would be best for her (again, this must be done on neutral territory). Baby piggies need constant companionship and social interaction from another.
No your cage isn’t too small - six piggies only ‘need’ an 8x2 (although bigger is always better) so you have more than enough space for them.
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