Havana Brown kittens & cats in Charlotte, Michigan

I adopted Nova Star in December of 2023. I used the Jackson Galaxy method of introducing 2 cats to make sure my first cat and her had the best possible start on their friendship. Unfortunately, that never happened. I tried for 4 months but they still hiss and scrap with each other. Nova has gotten her face scratched several times during these tussles. After 4 months, I just let them figure things out but I'm concerned Nova might get seriously injured. Nova is very particular about where on her body she likes to be scratched. She gives very clear signals when she wants you to stop. She has her claws and she's almost 4 years old. She definitely likes to be inside, though she does explore the catio occasionally. She would make someone a great only cat, though she may be okay with male cats, I'm not sure. She may also be fine with older kids or dogs. I've never had her around them however.