It's possible that Isis will never tolerate Camille. Or she might eventually become happy to have her company when she gets old; I've had that happen with a pair of male cats. I've also had a male cat (who had lost his sibling) immediately take to a younger male cat that we adopted so he'd have company. Jealous females are the worst, though, imo. I've never had any luck convincing one that she should put up with a cat she had decided not to like.
I guess cats are no different than people. They have different personalities and there's no telling in advance who they're going to be friends with.
Catloverami has some really good suggestions. Maybe they will help.