As you said, the animosity might be two sided. Buuuuuuuut, in such situation, both parties often blame the other one. The biography of my character, which is written from Irea's point of view, is written with Irean point of view. Of course, in general, they will blame Renais. From a character having Renais point of view, things might not be exactly the same. :P THat is what will create sparkles when two characters meet.
Now I remember that character! I was mixing her up. What I actually said at the time was that she could flee to join Irea, but that she could also stay and be a part of your group so we can have more characters in common. I was not decided yet, but you seemed to have understood it was a given she'd join Irea. Probably because of something I must have wrote. So...yeah, not quite decided yet. It's true that I won't have many characters on your side, so it could be good if I changed that. About her age though...I guess that if she flees, one way or another, she would have to be young. In order to abandon all of your history and responsibilities behind without thinking of the consequences or even what it all really includes, people have to be young. I'd say she would be about 16-17 years old, still acting on emotions before thinking.