My husband and I have been trying to introduce our current cat who is about 4-5 years old to a 4 month old kitten. They are both females and we honestly feel like it has been getting worse. The first week or so we did not let them visually see each other, just be heard through the door. Our resident adult cat thought something was off since we started to shut the office door where the new kitten resides. I then started to drop treats near the door, began feeding them through the door, there were hisses from our resident cat but after a few days I was able to move her closer and even open the door a bit so they can see each other (before that I have been doing so much scent swapping with blankets/toys/etc and our cat just hisses/growls and swishes tail low and aggressively). It’s been about 2 weeks and we moved to feeding them In the same room but we have to hold the kitten since I get a sense that we should not trust her to roam around alone, I feel our cat would hurt the kitten (we are not able to clip her nails as she gets soooo aggressive and she bites, she is the type of cat that lets you know when she’s had enough and she huffs a lot). Our resident cat will also try to bang on the door the kitten is in so we have started to let her in while we hold the kitten and she watches, but our cat is just going in there for food and will full on aggressively hiss and today we tried to distract them by play but our cat cannot be distracted- they were about 6ft apart and our older cat tried to lunge with her teeth at the kitten. Since then they have been separated again and she remains to have access to the house while the kitten remains in her safe zone. We are becoming SO discouraged and stressed over this and feel we cannot trust our resident cat’s aggressive behavior at the end of the day. Any advise would be so appreciated. Thank you!!!