Tonight, they met the new kitty - and brought life to the term "abject terror." Both bolted as far away as possible upon noticing the as-yet-unnamed cat. This included (for Roxy) jumping about four feet from my hands to the top of their cage. With Katzemaus in the room, they've remained frozen in position for a good ten minutes, not daring to move lest they grab her attention.
I'm starting to doubt they'll ever be best buddies. Poot.
On the bright side, at least Kitty A hasn't shown any significant interest in the rats. She wandered by the cage and gave them a cursory sniff, but that was about it. Perhaps it's because I told her if she eats one of her sisters, she'll be sorry.