I have had a guinea pig for a couple of months, and she is around three-three and a half months old. I have heard that it is better to have two, and have been contemplating buying another one. However, I have heard that at around five months they can be a little mean and fight. She has a pretty good temperament, aside from being kind of nervous still and can nip sometimes. How should i introduce a new guinea pig to her? What age guinea pig should I get to introduce her? Thanks!