Seems I'm going to have to remove Pippin from the trio, she has been acutely bullying Bailey for a while now but I hoped if allowed to assert herself over her submissive she would eventually calm down. That hasn't been the case sadly and tonight I found bites on Bailey's rear end and ear, they're not severe bites but signs that things are escalating rather than getting better.
Bailey is already such a timid little thing anyway, this won't be helping. I'm not sure what I will end up doing with Pippin, whether she will go with the herd and hopefully not cause world war 3, have a trial separation and retry them together, find her another friend and hope she doesn't bully her or just have her next to the others on her own.. lots of options, some less desirable than others but still options.