Are any of them neutered/spayed? If not, they would be happier and get along better if they were. I personally think it is very unfair to keep getting new ones and kicking them out. She probably does so because she wants to be the only inside cat and it has worked each time she has done it...you've gotten rid of the interloper. It also takes some time, patience, and finesse to introduce new cats to the Ones who already own us. The new one should be kept in a separate room for a few days with some way of the two being able to sniff each other, either under a door, through a screen door, or through one of them in a kennel. It is also very important to let your Current Owner know that you still consider her to be very important and love her just as much as ever. The other thing is she may not like males!**bg**