My friend uses the Feliway plug ins and swears by them. Repeating myself, but she started using them when she had to introduce a half wild barn cat into her family, which included three (I think) well established and situated cats. The new cat was an altered male, the three house kitties altered females. She loves Feliway, and always has a supply on hand. It is cheaper at valleyvet.com. It may be a bit easier/less threatening to introduce a male rather than a female. Just a thought...