Since your cat has had you and your family all to herself until now, this is a very normal reaction. I had the same experience when I added a second cat. Though it depends on the cat, it can take a while for your existing cat to adjust. It might take a few more weeks or months before the cat starts interacting with the new cat. I know it's difficult to think you've upset your cat by adding another, but in my experience, it's just a phase, and eventually, she'll get over it. I wouldn't consider finding a new home for the second one. Just give the situation more time and find ways to encourage interaction, play and a few cat treats.