I adopted a new female for my surviving female and they're both about a year old. I was warned my new adoptee had a rough past. She was brought to the humane society after a rodent hoarding situation (she had lived with other female rats during this), adopted, then brought back after "not getting along" with her cage mate. I was optimistic because she had a home for 9 months before I took her but she is just not about making a friend. She won't even tolerate their cages being next to each other without becoming stressed and showing dominance, and trying to introduce in neutral territory only resulted in blood. I'm at a loss. I don't want to give up but I also don't want to risk further injury to either of them. Any advice?