Sudden aggressive behaviour...help!

Hi everyone I need your help regarding my two babies.
Leelee is a one year old, pure white, green eyed, gorgeous British shorthair and Mollo is a ten month old, black and white beautiful cross breed.
They have been best friends since Mollo came to live with us at 10 weeks old.

Leelee was only around 5 weeks of age when I rescued her from a doorstep, freezing, wet through and starving. She settled well into our family and is a loving, affectionate lap cat.
Mollo is a little more independent but also loves her cuddles. She'll plonk herself on your chest ( usually when you're trying to read) and will curl up in a ball after giving you hundreds of head butt kisses!

These two babies used to play together, sleep together, eat together, do everything together but now, all of a sudden, leelee has decided she hates Mollo.
If Mollo so much as walks near to leelee, leelee hisses, smacks, scratches and bites her.
Mollo walks away not seeming to be bothered by it but it's got me concerned.

Neither have been spayed as yet ( both are house cats as I live right next to a motorway) but they are both booked in for next Tuesday.

At first I thought leelee's behaviour was down to her coming into season but she does it all the time whether she is in season or not.
It's been going on for three months.

I do at the moment have a stray female staying with me that just had kittens a few days ago
( she's been here for 11 days), but leelee isn't at all bothered by her or the babies. In fact she has welcomed the stray with open paws and will happily share her food, groom and snuggle with the stray.

What could have made her turn against her little friend, Mollo, so suddenly and cause her to be such a bully with her?
Any help would be massively appreciated.
Thank you
X

Hi @raebekah,  just reading this now, and hoping that the spay operations went well for both Leelee and Mollo, this past Tuesday.

I really think that Leelee is reacting to all the new and old scents that are going around in your home, right now, and will settle down, after her spay, and once her hormones settle down.

Cats have heightened senses, and can pick up on smells, touch, and noise, which we humans cannot.

Another reason a cat may suddenly and drastically change their behaviour, is due to ill health, but your vet would notice this, through the vet exam, and pre-op blood work.  I would not worry about health, as long as Leelee is eating well, using her litterbox, and basically acting/playing as before.

The stray mother cat that just had kittens could also be throwing the "usual cat dynamics within the home" off, and Leelee may be wanting to assert her dominance.

Give it some time, and just observe all your cats, and give all the cats equal playtime/attention and also quiet space, if they need it.

I'm so glad that you got your cats spayed, because even if they are indoor cats, they will be more comfortable by not going into heat cycles, and it prevents future health issues. Good going.