My cat got out of the house in October and brought home a 3 week old kitten. We took her in and cared for her while we tried to find out where she was from and if she was missed by someone. Learned she was a feral kitten and after talking to a vet decided to care for her and keep her in our home where it's warm and safe. She's now 14 weeks old and has gone from being a little cautious of us but still letting us pet her to running anytime we are in the room. She used to be fed by me by hand and now she's terrified of yhe sight of me. She loves our male cat that brought her home though. They are best buddies and are always playing and cuddling. He isn't much older than her so he's very happy to have a playmate and we love her. She's our skittish cat even if she never warms up to us but we hoped eventually she'd at least be okay in the room with us even if she isn't a cuddly lap cat. (The male is neutered and baby kitten has her appointment to be spayed in January so no worries of them having kittens🐱)
Try giving the kitten a few elevated resting places,they should be as high up as your upper body when you stand.
The resting places needs to be in a place where your cat can see what is going on in the room,it is best if it is a place a bit out of the way so you avoid walking by all the time.
Try to get the kitten to play a few times a day as this can help getting your cats stress level down,it is best if you can make the play time before you feed her so you make a routine play,eat,sleep as this is a cat`s normal rythm.
Make sure the cat can get away from the situation if she wants to,try to avoid your cat feeling trapped,a cat likes to be in control of the situation.