Some cats just never warm up to each other. My second oldest (Ginger) and youngest (Krissy) don't get along. I would be thrilled if they just tolerated each other, but it has been war for the past 8 years. We give Krissy her own area when we leave the house or she would be a basket case because Ginger is relentless in her hunt for poor Krissy. What Krissy doesn't know is that Ginger is a total coward and if she just showed some moxie, Ginger would back right off.