New mama (stray) becoming aggressive toward other cat

I got Shareena when she was 7-1/2 weeks old and her sister six weeks later. The fought for two days until they figured out who was top cat (Shareena), and they've been best friends ever since. They are now 17 months old.

A couple of months ago I took in Goldy, a pregnant stray who was probably around 7-8 months old at that time. My two touched noses with Goldy and then mostly ignored her. I saw an occasional soft hiss or a bop on the head with claws in from Shareena, but nothing major, and Goldy never reacted at all.

When the kittens were born September 23 Shareena suddenly became hostile: hissing, scratching, biting everybody including me. She has settled down now and is almost back to her normal self with me, but still hisses at Goldy some.

Shareena has never harmed the kittens. She looks into the laundry basket where I've been keeping them but doesn't climb into the basket. When I have them out on the floor she will start grooming them, cleaning their faces or bottoms. This does not seem to upset Goldy at all, she just lays there and watches. Then when the kittens come back to her she cleans them again.

The change that I've noticed is that when they are in a different room from the kittens, Goldy is hissing and growling at Shareena and sometimes chasing her through the house.

Is there anything I can do to get them to be friends, or at least not be enemies? Goldy is normally a sweetheart and I would love to keep her. However, if she is going to continue upsetting Shareena I'm afraid I'll have to find a new home for her along with her kittens.

Bumping this back to the top

The vet won't spay Goldy until she's completely weaned the kittens, which won't be for another 6-7 weeks. I was hoping there might be something I could do in the meantime.

Also, I thought it was a little odd that Goldy would let Shareena groom her babies and only attack her when she was in another room away from the babies.

She has never attacked Miss Patchwillow, but I suspect that is because Miss Patchwillow is much more timid and rarely takes the role of alpha cat.

Oops! Meant to say the kittens were born August 23. There doesn't seem to be an edit function on this thread.