[Kaylee]

This morning and tonight Millie one of our cats has been acting out of character. Its almost like shes mad at me. We have had a change in the house being Sophie a 12 week old kitten who we have had for 3 weeks. We introduced them about a week and a half ago and they do get along but Millie does give her a tap when shes being too rough. I don't think its because of Sophie as she gets the same amount of attention as before if not more since Sophie has come home, same goes for our other pets. At the same time though I wonder if maybe shes a little jealous because apart from me everyone else doesn't really pay much attention to her. Although thats due to her mostly being in my room as shes very shy and has formed the strongest bond with me. This morning though and tonight she has acted completely out of character. She actually swatted at me and attacked me something she has never ever done before. While normally she would come up to me and lay down and purr while licking me and being her sweet self she has just been attacking me and swatted at me while growling and hissing at me.
Has anyone else ever had this happen before or have any ideas as to why she may be acting like this?

 

[somebody]

Change is very difficult for many cats, and a new kitten can cause a lot of stress. Just because she seems to have accepted Sophie, it may be bothering her more than you've realized.

Stress can make a cat sick, and any change in behavior can also indicate sickness or pain. The first thing to do is to take Millie to the vet for a complete check up. Have a urinalysis done, she may be developing a urinary tract infection (a common illness brought on by stress)

Have you had a chance to observe her litter box habits to see if there is any change in her peeing or pooping?

 

[Kaylee]

I have wondered if shes possibly feeling jealous as shes an older cat being 7 years old with a not so great past.
However today she has seemed to be almost like her old self. She greeted me and actually licked at me today so I'm also wondering if perhaps she was just in a bad mood yesterday as that was the first time she had ever anything like that.
Shes actually due for her feline leukemia test tomorrow so when we take her in for that we have our vet check her over.
I'm not sure if anyone else has noticed her litter box habits apart from me but everything is still normal.