My cat is around 8 years old. She's absolutely the sweetest cat pretty much only towards me. She'll groom me non stop if left unchecked, sleeps on my desk all day while I work ect...

However towards my partner, her kid or nearly anyone else she just can't even. She'll hiss at anyone else and for the last 2 years when my partner and her kid come over my cat will basically exclude herself and pretend they don't exist. We all just moved in together and my cat is really not doing well with it. She is only happy if it's the two of us and I am running low on ideas to figure this out.

My cats background if it helps: she's been my cat only since right before the pandemic, prior to that I lived with her for around two years as she belonged to an ex-partner when she and I parted ways she insisted I keep the cat because she's miserable without me. Her ex was rather abusive and likely harmed the cat at some point.