My cat passed away, and one of our other cats seems to be replacing her.

As the title says, I’m wondering if someone can explain this to me,

My cat passed away very suddenly. Took her to the vet and they said she’d need to be put down. We have 2 other cats, which are actually her daughter and grandson respectively (I lost my job shortly after I got my cat due to my depression, didnt know I could sterilise her so young so she got out and had kittens.) one of her kittens got really sick and I nurtured her and took care of her, and eventually she was given to my little sister as we decided to keep her. Gave the other kittens to close friends We were still under the misconception that cats couldn’t be sterilised until theyve gone through their first heat, but like her mother she got out and got pregnant and respectively had her kittens and we kept one as well. So yeah, 3 generations of cats lol They’re all sterilised, all is well. I just misunderstood a vet some time ago and thought she said cats couldn’t be desexed until they’ve had their first heat.

Anyways. My cat passed, and now her daughter, my sister’s cat is clinging to me. She comes and sleeps on my bed, she eats my cat’s leftover biscuits, shes almost always in my room. Part of me doesn’t like it, I assume shes “marking her territory” now that my cat is gone and I feel like she’s erasing my cat, while my dad thinks she misses her mum. It’s a nice thought, but they often lashed out at each other lol. So I doubt it.

I was just wondering if anyone could explain this, is it a territorial thing? Is she mourning…? I don’t know how to feel about it.