I know what you mean. I have never done a trio, just pairs, although I had a pair of sisters who took a bereaved male under their wing and it took a good few days before they allowed him into their bed which was in the shed. They accepted him in their run but he wasn't allowed in their bed straightaway. It does take time for rabbits to accept one another because in the wild they are in family groups and outsiders are not welcome as they are a threat to their territory and food. So in your case I would definitely keep goin for a few more days, as long as they aren't hurting her. Sometimes what looks like unfriendly behaviour is just normal for rabbits.