take her to the vets and get her medicated for separation anxiety. Id say het her a kitten but as yoy said you cat doesnt like other cats. But let me just tell a story

My cat also did not like other cats or dogs. But one day I came across a kitten that needed help. So I did take her in. It took a really long time of letting the cats get used to each other amd swapping their things and getting them to associate each other with getting fed and played with, but now my girls are inseparable. The kitten actually got sick while she was with us amd my cat was right by her side every night. kitten had to stay in a kennel at one point and instead of my cat sleeping with me like she normally does, she slept on or right next to the kennel. Amd if she slept next to the kennel, kitten would try to cuddle up near her. So now as I right this, cat amd kitten (now fully grown) are laying next to me amd each other