Well Uncle, I had that problem once (more than that actually, but this tory fits the best). We had this Calico named Molly, then one day I was coming back from making a school run, on a very rainy day. Got stopped in traffic at a stoplight and suddenly I saw this little furball go under my van from the front. I ju mped out (pouring down rain) because I knew that it would be flattened almost instantly. It was going toward the back of my van, so I went back to the rear of the van only to find that the kitten had disappeared! So, I cautiously drove to a carwash nearby, to look for the kitten and not get any wetter than I already was. I finally located the kitten, went by McDonalds, got some milk, took it home and told my wife (Brenda) that we needed to find a home for it because I knew Molly wasn't going to get along with it and I was right. Everytime we went ANYWHERE, we had to take Joy (the kitten) with us or Molly would terrorize it. Now, the funny thing is that, as Joy grew up and got to be bigger, she was less and less afraid of Molly and after a while, the tables started to turn and it wasn't long before Joy was Terrorizing Molly!
Now, they both are old enough and pretty good size and are just pretty well laid back. I really didn't know if old Molly was gonna live long enough for Joy to back off or not. She really spent some time getting back at Molly for all those times that she terrorized her.