Years ago, I got Mobius when I had Smokey the Elder. I didn't have anywhere to isolate the kitten who was 4 months old at the time. I just kept a wary eye on them and the squirt bottle handy if there ever was any serious fights. There was much growling, hissing and posturing on Smokey's part, for a couple of weeks. Then one night I got home, and they were arm-in-arm cuddling on the couch! Someplace I have a film pic that I should scan in if I can ever find it.

There is hope for even a princess to make friends. Just give it time. It sounds like it's actually going OK.