I have a three year old female who, since at nine months has been with me (only). I just brought home a second female, Lillian, age ten years, who lived with nursing home residents for years. My current cat, Sophie, will not accept another in HER house. I've been taking steps at introducing, as I've read to do. It's been three weeks and I still have to keep them separated. One glance and Sophie starts growling and hissing again. How long does it take, or should I try to find another home for Lillian?