Have you considered fostering? Shelters are often in dire need of foster homes for cats and kittens. That would be a great way to help a cat in need while also gauging how Tiffany would feel about a kitty companion.
If you haven't yet, read over some guides about introducing cats. Here's one from a website I like: http://www.catster.com/kittens/How-to-I ... Feline-123
I have two cats and they are both around 2-3 years old, one male, one female. I had Luna first, and then Dexter showed up on our porch and I knew he was meant for us. It took about four months for them to really warm up to each other. They still fight now and then, but they also groom each other constantly and hate to be away from each other so I know they are really BFFs. Cat friendships take time, even if you follow all of the right steps, but I think it can be really rewarding for a cat to have a companion.