**"I wanted a companion for Sausage, not a roommate situation where they tolerate each other."**

A common misconception is that cats that are cuddly or groom each other are being friendly, while cats that merely are in the same room are just tolerating each other. Cats might also socialize by following each other around and being in the same place. If you find your cats all sleeping in the same room regularly, that's not just because they merely tolerate each other. Your cats already get along quite well for only having met for a week if they sometimes sleep or relax in the same space. 

However, as it's only been a week, I think Peach is still nervous. This situation will be scarier for her than for Sausage. He is in confident because he's in his home territory.  Likely even the room you are keeping Peach in still smells like him. Peach, meanwhile, has very little that she feels like is hers. It's a much more anxious sort of situation for her. Her hissing, growling, and swatting at Sausage are all signs that she's still a bit nervous around him. I think it's likely she'll calm down eventually, and you may even see some of the friendlier behavior she's shown with other cats, but it also might need a little human intervention:

* **Start spreading her smell around the house more.** 

If there's something in her room that she's used a lot, then put it in a place in the rest of the house in a place that Sausage frequents. You want to really get her smell mixed in to help her gain confidence.

* **Give Peach better ways to get away from Sausage.** 

Incidents are happening on the cat tree because she probably feels safer up high, but then when Sausage approaches it, she is now trapped with no way down. You should instead make it so there is another piece of furniture she can go to from the cat tree, that leads to a different route she can go to get down and away from Sausage. Arrange your entire house this way if you can. This way Peach can choose when she wants to interact with Sausage, and avoid him if she doesn't. With fewer negative incidents happening, it'll hopefully help to build up her confidence around Sausage.

* **Play with them together.**

It also might help to build up Peach's confidence to play with both cats together. You might need a helper to do this, so one person can play with each cat. It will encourage them to be close together, but they will be focused on the toys and not each other.

**And, yes, definitely get Peach fixed.**

Though unfixed toms are more notorious, unfixed female cats can also be more aggressive or territorial than fixed females. It's better for her health and will make her more companionable.