I have a female house cat who is about a year old.  I also have
several outdoor "farm" cats.  (this is a farm).  On several occasions
one of the outdoor cats have gotten in the house, and my indoor cat
gets nasty and hisses, etc.  (normal thing cats do).  Recently I
discovered several newborn kittens in the barn, which indicates there
was a stray tomcat around (all my males are fixed).  These kittens are
now big enough to be eating on their own, so I decided to bring them
in the house.  My indoor female cat went hysterical.  Not just the
usual hissing like at the adult cats the sneak in once and awhile, but
she just went crazy, and attacked one of the kittens, and would have
probably hurt the kitten had I not stopped the attack by dousing the
female with her water bowl.

What's with this?  I had expected her to get along with them better
than with an adult cat, or at least treated them the same.  I dont
like this at all, in fact I am considering finding a new home for the
cat, if this is how she is, and will keep the kittens instead.  She
was downright nasty.

Any ideas?

Thanks