From the Editors of The Daily Cat
Take a deep breath and relax because things are not as bad as they seem. Ginger's reaction is very normal for a cat whose space has been invaded.
Start from scratch and do a reintroduction. As you introduce the kittens to Ginger this time, though, do it in brief sessions of positive association. Let Ginger see the kittens for a few seconds and then offer her a treat or distract her with a toy. Do several 10-to-20 second sessions so Ginger learns that good things happen when she's in the presence of the kittens. These brief sessions will also help her to not feel so threatened. The key is to give Ginger a reason to like the kittens. After the introductions, put the kittens into another room away from your adult cat. Let them have their own spaces for a week or more, as long as it takes for Ginger to become accustomed to having other felines around.